Resolving STEP 7 V5.5 NetPro Freeze and Crash on Startup

1. Problem Overview

SIMATIC STEP 7 V5.5 (including the V5.5 Professional package) is a multi-component engineering suite whose core editors (KOP/AWL Editor, SCL, Graph, PLCSIM, Teleservice) generally load and operate from a single installation tree. NetPro — the Network Protocol configuration editor used to build PROFIBUS, MPI, Industrial Ethernet and sub-net topologies for S7-300, S7-400, PC stations, and SIMATIC Net components — is one of the most dependent subsystems in the suite. It relies on a stack of legacy COM/ActiveX controls (OCX), shared runtime DLLs, and a registered automation interface that talks to HW Config and the S7 project database.

The failure mode documented in the field is unambiguous: launching NetPro either causes an immediate hang (the splash or network canvas appears for a few seconds, partial participating-station graphics render, and the process stops responding) or an outright process termination. The Windows Task Manager reports the executable S7WNPROX.EXE (or S7NETPRO.EXE in older builds) as Not Responding, and the application must be killed. All other STEP 7 tools, including HW Config, continue to function normally. The same symptom appears in freshly created *.S7P projects and in legacy projects that previously opened cleanly under STEP 7 V5.4 SP5.

This article documents the diagnostic path, the most common root causes encountered in the field, and the resolution procedures that consistently restore NetPro operation without requiring a full Windows reinstall.

2. Symptoms and Failure Modes

NetPro failure on startup presents in one of three observed patterns. Identifying the pattern is the first triage step because it points to a different root-cause family.

Patterns A and B dominate the reported cases. Pattern C is rare and usually signals that a Windows update or a third-party installer has overwritten one of the legacy OCX controls shipped under STEP7\S7BIN or ...\S7LIB.

3. Root Cause Analysis

NetPro is built on top of Microsoft COM and depends on a stable set of registered controls. The most frequent root causes, ordered by prevalence in the Siemens support record and independent field reports, are:

1. OCX / DLL registration drift. After a Windows update, a Security Suite install, or a manual cleanup, the registry entries for S7wnprox.ocx, S7netprox.dll, mscomct2.ocx, comdlg32.ocx, tabctl32.ocx, comct332.ocx, and msinet.ocx can be de-registered or pointed to the wrong file version. NetPro is the only STEP 7 tool that loads all of them in a single pass at startup, which is why it crashes first while KOP, SCL, and PLCSIM continue to work.
2. VMware virtualization interference. A VMware Bridge Protocol or VMware NAT service can install a virtual network adapter that registers as an MPI/PROFIBUS-capable interface inside the Windows network stack. NetPro enumerates all network adapters and COM ports to populate the network/subnet tree; when a VMware adapter is misregistered or its service is stuck in a starting state, the enumeration loop hangs.
3. Internet Explorer version skew. NetPro internally hosts the Web-based components of the SIMATIC documentation and the Online Help via the installed Internet Explorer shell (the shdocvw/mshtml engine). IE 8.0.6 on Windows XP SP3 is the highest supported IE for STEP 7 V5.5; downgrading after an IE update, or installing IE 9/10/11, can break the embedded browser host.
4. PCS 7 / WinCC / other SIMATIC add-ons. PCS 7, WinCC flexible, or other SIMATIC packages install shared OCX files into %SystemRoot%\System32. When a PCS 7 trial is installed over a STEP 7 V5.5 environment, the version reference of shared files can be overwritten. NetPro, which depends on the STEP 7 reference, then fails to load.
5. .NET Framework removal or rollback. Several STEP 7 V5.5 dialogs (NetPro's Connection Diagnostics, in particular) call into managed code through a COM-to-.NET interop layer. Removing or downgrading the .NET Framework — for example by running a Microsoft .NET cleanup tool — breaks the interop bridge even when the STEP 7 installer thinks the prerequisite is met.
6. Project-side corruption. A *.S7P or *.S7L file that contains a reference to a removed GSD file, a deleted SIMATIC PC station, or a library version no longer present on disk can trigger a long enumeration before NetPro hands control to the user. The user observes this as "draw of participating stations, then freeze."

4. Pre-Diagnostic Checklist

Before touching the system, capture the following information. It isolates Pattern A/B/C and determines which resolution branch to take.

5. Step-by-Step Resolution

Work the steps in order. Each step ends with a verification action. If verification fails, continue to the next step rather than retrying.

5.1 Stop non-essential services and background tools

1. Open services.msc.
2. Stop and disable (temporarily): VMware NAT Service, VMware DHCP Service, VMware USB Arbitration Service, VMware Workstation Server.
3. Stop antivirus and firewall real-time components (Symantec, McAfee, Trend Micro, ESET, Kaspersky). NetPro loads many OCX files; aggressive AV hooks on scrrun.dll and mscomct2.ocx are a known cause of hang-at-startup.
4. Open SIMATIC Manager, load a small test project, and launch NetPro.

Verification: If NetPro opens cleanly, the conflict was VMware or AV. Re-enable services one at a time to identify the offender.

5.2 Re-register the NetPro-dependent OCX and DLL set

This is the highest-yield action when Pattern A is observed.

1. Open an elevated command prompt: cmd → Run as administrator.
2. cd /d "%SystemRoot%\System32"
3. Unregister the STEP 7 OCX set first to clear stale entries:

   regsvr32 /u S7wnprox.ocx
   regsvr32 /u S7netprox.dll
   regsvr32 /u mscomct2.ocx
   regsvr32 /u comdlg32.ocx
   regsvr32 /u tabctl32.ocx
   regsvr32 /u comct332.ocx
   regsvr32 /u msinet.ocx

4. Re-register from the STEP 7 binary directory (not from System32, the canonical copies live here):

   cd /d "C:\Program Files\Siemens\Automation\STEP7\S7BIN"
   regsvr32 S7wnprox.ocx
   regsvr32 S7netprox.dll
   regsvr32 mscomct2.ocx
   regsvr32 comdlg32.ocx
   regsvr32 tabctl32.ocx
   regsvr32 comct332.ocx
   regsvr32 msinet.ocx

5. Launch NetPro from SIMATIC Manager → Options → Configure Network.

Verification: A successful regsvr32 call returns DllRegisterServer in <file> succeeded. A 0x80004005 or 0x80070005 error means the file is locked by another process or the user lacks rights.

5.3 Remove the VMware virtual network adapters from the NetPro scan

1. Device Manager → View → Show hidden devices.
2. Under Network Adapters, identify every VMware Accelerated AMD PCNet Adapter, VMware VMCI Bus Device, and VMware Virtual Ethernet Adapter for VMnet#.
3. Right-click → Disable (do not uninstall — preserve for the VMs).
4. Open ncpa.cpl, confirm the VMware bridge is unbound from any physical NIC.
5. Open NetPro → Options → Set PG/PC Interface. Reset the interface assignment to the physical CP (e.g., TCP/IP → Intel PRO/1000 MT Desktop Adapter).

Verification: NetPro's Participating Stations list should refresh without the VMware adapter appearing in the interface drop-down.

5.4 Re-establish Internet Explorer 8 baseline

1. Confirm IE version. STEP 7 V5.5 documentation and NetPro Online Help are designed for IE 5.5–8.0; IE 9+ breaks the embedded browser host.
2. If IE has been upgraded past 8.0.6001.x, roll back via Programs and Features → View installed updates → uninstall the IE 9/10/11 update.
3. Reset IE settings: Tools → Internet Options → Advanced → Reset.
4. Re-register the IE COM shims:

   regsvr32 mshtml.dll
   regsvr32 shdocvw.dll
   regsvr32 urlmon.dll
   regsvr32 mshtmled.dll

Verification: Open SIMATIC Manager → Help → Contents. If the HTML help tree renders, NetPro's internal HTML host is restored.

5.5 Restore the .NET interop prerequisite

1. Open Programs and Features.
2. Confirm the presence of Microsoft .NET Framework 2.0 SP2, 3.0 SP2, and 3.5 SP1. These are the .NET versions that STEP 7 V5.5 installs as prerequisites.
3. If a cleanup tool was used and 2.0/3.0/3.5 are missing, download the dotnetfx35.exe redistributable and reinstall.
4. If only 4.x is present, install 3.5 SP1 — it ships as a side-by-side version and does not conflict with 4.x.

Verification: dir /b %SystemRoot%\Microsoft.NET\Framework should show v2.0.50727 and v3.5.

5.6 Isolate project-side corruption

1. Copy the suspected *.S7P project to a working folder.
2. Open with File → Open → Project in a fresh SIMATIC Manager session with no other STEP 7 instances running.
3. If NetPro hangs on a specific project but opens with the bundled STEP7\Examples project, the issue is in the project database:

• Re-attach missing GSD files: Options → Install GSD File.
• Re-install any referenced SFB/SFC library via Options → Install Library from the original STEP7\S7LIBS media.
• Recreate the SIMATIC PC Station by removing and re-inserting the station under HW Config — this rewrites the PC interface assignment that NetPro reads on first open.

Verification: NetPro must open with the same project within 3 seconds after SIMATIC Manager → Options → Configure Network.

6. DLL/OCX Re-registration Procedure (Reference Table)

Use this table as a checklist when scripting a batch re-registration. Always run the unregister pass first; never skip it, as it clears the negative-cache entries Windows uses after a load failure.

7. VMware and Virtualization Interference

VMware Workstation, VMware Player, and the VMware Bridge Service install kernel-level drivers and virtual NICs that are visible to the Windows network stack as physical-style adapters. NetPro enumerates the Windows network configuration at startup to populate the PG/PC interface assignment and to discover CPs that can be assigned to a station. The VMware adapters, if present, are evaluated as if they were real Industrial Ethernet or MPI interfaces. When the VMware virtual adapter service is in a transitional state — typically because a VM was suspended, the host was resumed, or VMware was partially uninstalled — the NetPro enumeration call GetAdaptersInfo() blocks for up to 30 seconds, which the user perceives as a freeze.

The same effect can be produced by Hyper-V's Virtual Switch adapter, VirtualBox's Host-Only adapter, and Windows VPN clients that install a virtual TAP adapter (Cisco AnyConnect, GlobalProtect, Pulse Secure). The diagnosis is the same: disable every non-physical adapter under Device Manager, restart SIMATIC Manager, and test NetPro. Re-enable one at a time to find the offender.

8. Windows OS and Internet Explorer Compatibility

Siemens certifies STEP 7 V5.5 + SPx for the following Windows baselines:

Running STEP 7 V5.5 on Windows 8 / 8.1 / 10 / 11 is possible under compatibility mode but is not certified and produces intermittent NetPro failures because the modern Windows network stack returns adapter metadata in a different format that the NetPro COM host does not understand. If a Windows 10/11 install is unavoidable, use the bundled S7WINADMIN script to grant full control to the STEP 7 directories and run SIMATIC Manager in Windows XP SP3 compatibility mode.

9. PCS 7 and Other SIMATIC Component Conflicts

PCS 7, WinCC flexible / TIA, Drive ES, S7-PLCSIM, and the SIMATIC NET PC Software share several OCX controls and helper DLLs with STEP 7 V5.5. Installing PCS 7 trial over an existing STEP 7 V5.5 install is the single most common cause of NetPro freeze in the field.

The fix path is ordered:

1. Uninstall the PCS 7 trial via Programs and Features using the original installer media's Setup in maintenance mode, not the Windows uninstaller alone.
2. Run the Siemens S7SETUP.EXE from the STEP 7 V5.5 DVD in Repair mode. This restores the original OCX versions under STEP7\S7BIN and re-registers them.
3. Re-run the OCX/DLL re-registration steps from Section 5.2.
4. Validate with a clean example project before opening user projects.

10. Verification Matrix

After each fix attempt, validate against this matrix. NetPro is considered fully restored only when every row passes.

11. Prevention and Hardening

Once NetPro is operational, lock the configuration to prevent recurrence:

• Disable Windows Auto Update for the OCX-class components. Use a WSUS policy that allows security updates but blocks the Windows 10 Upgrade push and IE version upgrades.
• Exclude STEP 7 directories from antivirus real-time scanning: C:\Program Files\Siemens\Automation, C:\Program Files\Siemens\Step7 (varies by install path), and the S7BIN, S7LIB, S7FIRMOS, S7DATA subfolders. Exclusions on scrrun.dll, mscomct2.ocx, and S7wnprox.ocx are particularly important.
• Snapshot the registry after a known-good install: export HKLM\SOFTWARE\Siemens and HKCR\CLSID for the OCX set above. A corrupted workstation can be restored in under 5 minutes by re-importing these keys.
• Avoid layered virtualization. Do not run STEP 7 V5.5 inside a VM that itself uses a bridged virtual adapter for the host's physical NIC; the NetPro adapter enumeration will misbehave. Use NAT or Host-Only mode and pass through a USB CP (e.g., Siemens CP 5711) via USB passthrough instead.

12. Escalation Path

If the matrix in Section 10 still fails after the full procedure, escalate with this evidence package to Siemens Technical Support (Industry Online Support, Product: SIMATIC STEP 7 V5.5, Component: NetPro):

1. Output of winver, regedit /e step7reg.txt "HKLM\SOFTWARE\Siemens", and sc query type= service state= all > services.txt.
2. Event Viewer → Application → Application Error entries for S7NETPRO.EXE with the Faulting Module name and offset (hex address).
3. Dr.Watson / procdump -ma -e 1 -f "" S7NETPRO.EXE capture from Sysinternals.
4. Output of regsvr32 S7wnprox.ocx with the success/failure code.

With this data, Siemens support can determine whether the failure is in the STEP 7 binaries (requiring an SP upgrade or hotfix) or in the OS / virtualization layer (requiring a configuration change), and they can issue an OSS / Hotfix reference if a known defect is matched.