Resolving PCS 7 OS Client SDB Conversion Failure in NCM

1. Problem Summary

The error sequence reported in PCS 7 V9.x projects typically surfaces in three layers:

1. WinCC Explorer OS Project Editor / Target System → Configure returns "Cannot access the target computer" even when the load path of the target computer is defined.
2. SIMATIC NCM (Network Component Manager) diagnostic viewer displays "General IE – message cannot convert an SDB" when trying to compile the PC station.
3. The OS load log (e.g. OSC13_Load.log) terminates with Warning: Error changing the computer name in the project in OSC13! followed by Warning: OS loading failed. Duration: 00:12:22 and Cancel: An error occurred while loading the target system!.

All three symptoms are produced by the same underlying fault: an OS Client (OSC) has been configured with an IE General interface and a PC Station, but no valid SDB can be generated because the OS Client does not own a SIMATIC NET PC station of its own. The SDB (System Data Base) is the binary block that STEP 7 / NCM distributes to PROFINET and Industrial Ethernet nodes to describe the network topology, IO devices, connections, and ports. When NCM attempts to compile the OSC station, it has no AS-IO targets to address and no S7 connections to enumerate, and the SDB build is aborted.

2. PCS 7 OS Architecture Overview

A correct PCS 7 OS deployment distinguishes between three PC roles. Misconfiguration between these roles is the leading cause of the SDB conversion fault described in this article.

The OS Client obtains all of its connection information from the OS Server Package (a .pck file generated on the OS Server and assigned to the OS Client). It does not require its own S7 connection configuration, its own AS symbols, or its own PC Station in NCM. This is the design rule referenced in the Siemens PCS 7 Compendium Part A – Configuration Guidelines.

3. Root Cause Analysis – Why the SDB Cannot Be Converted

When you insert an OS Client into the multiproject and add a PC Station with an IE General interface to it, NCM tries to perform the same compile workflow that is used for OS Servers and ES stations:

1. Resolve the assigned AS subnet.
2. Enumerate S7 connections, IO links, and published partner interfaces.
3. Write the resulting SDB / SDBX file to %ProgramData%\Siemens\Automation\NCM\S7ONLINE\SDB\<xxx>\.

Because the OS Client is supposed to be address-less at the S7/PN level, the enumeration returns an empty graph. NCM then raises the diagnostic Cannot convert SDB at the IE General level, the PC Station StationManager index reports as unreachable, and the WinCC loader cannot reach the target computer over the Station API.

4. Correct PC Station Configuration for an OS Server

The OS Server (single-station or paired with an AS station) must keep a full PC Station. The configuration is created in HW Config / NCM of the OS Server, then downloaded using the SIMATIC Manager → PLC → Configure command, or in TIA Portal V17+ the equivalent Download to target system action on the PC Station.

1. In the multiproject, open the OS Server PC Station (e.g. OS-Server1).
2. In HW Config, insert a SIMATIC PC Station and add the components in this order:
     a. WinCC Application (slot 1) – version matching the OS Server project.
     b. IE General or CP 1623 / CP 1628 (slot 2) – the Industrial Ethernet interface bound to the terminal bus / plant bus.
     c. Station Manager (index 125 in the loader log) – automatically created.
3. Set the IE General's IP address and subnet mask to the terminal bus subnet (e.g. 192.168.0.10 / 255.255.255.0) and the MAC address assigned to the NIC.
4. Compile and download the PC Station. This generates the SDB that the OS Server will use at Runtime.
5. Define the load path of the target computer: WinCC Explorer → OS → Target system → Load path, e.g. \\OS-Server1\WinCCProj\OS_Server1\.

For the OS Server PC Station, the SIMATIC NET PC Software – Configuration Manual is the authoritative reference for component ordering and SCE download order.

5. Correct Configuration for an OS Client (the Fix)

The OS Client must be a client-only node. The required configuration in the multiproject is intentionally minimal:

1. In SIMATIC Manager, right-click the multiproject and choose Insert OS → OS Client. Name it (e.g. OSC13).
2. Open the OS Client's Computer object (not a PC Station). Set the computer name to the runtime machine's hostname and the path to the target computer to a UNC path the loader can reach, e.g. \\OSC13\WinCCProj\OSC13\.
3. Assign the OS Server: in the OS Client's Server Assignment dialog, reference the OS Server (e.g. OS-Server1) and the symbolic server data. This is where the OS Server package (.pck) is consumed.
4. Do not insert a PC Station on the OS Client.
   Do not insert an IE General on the OS Client.
   Do not attempt to configure the OS Client through PLC → Configure in HW Config.

6. NCM SDB Generation Procedure (OS Server / ES only)

The SDB is generated by NCM during the PC Station compile step. The procedure is described in the PCS 7 Compendium Part F – Commissioning and the SIMATIC NET S7 Programming Interface manual.

1. Open the PC Station of the OS Server in HW Config.
2. From the menu choose Station → Save and Compile. NCM produces the SDB container under:
   %ProgramData%\Siemens\Automation\NCM\S7ONLINE\SDB\<online path>\
3. Open Station Configuration Editor on the OS Server. Verify that the components WinCC Application, IE General / CP 16xx, and Station Manager are listed and the diagnostic state shows a green check.
4. From SIMATIC Manager, right-click the OS Server PC Station → PLC → Download to Target System, or in TIA Portal use the PC System → Download action. The compiled SDB is pushed to the target's SCE registry at:
   HKLM\SOFTWARE\Siemens\Automation\Networks\<index>\SDB
5. Confirm the SDB with pgNumlc.exe /list or NCM diagnostic viewer: the IE General entry should report SDB OK, not SDB convert error.

7. WinCC OS Loading Procedure

After the OS Server PC Station is configured, the OS Server project is loaded before any OS Client. The sequence follows the SIMATIC NET – Commissioning PC Stations manual.

1. Open WinCC Explorer on the ES → open the OS Server project.
2. OS → Target system → Load path = \\OS-Server1\WinCCProj\OS_Server1\.
3. OS → Target system → Configure – this writes the SDB-aware PC Station configuration to the SCE of the OS Server.
4. OS → Start OS Runtime (with delay) after a successful compile.
5. On the OS Server Runtime PC, generate the Server Package via OS → Server Data → Export / Generate. Save the .pck file to a share the OS Client can read.
6. On the OS Client, import the package via OS → Server Data → Import or drop it into the Packages folder. Restart WinCC Runtime.

A correct load log should not contain the messages Error changing the computer name, StationManager(index 125) unreachable, or Cannot access the target computer. If any of these reappear, return to Section 5 and verify the OS Client has no PC Station attached.

8. Station Configuration Editor Verification Matrix

The Station Configuration Editor (SCE, SIMATIC Shell → PC Station Properties) is the single source of truth for what the WinCC loader will see on the target. Mismatches between HW Config and SCE are the most common cause of StationManager(index 125) unreachable.

The SCE reads its inventory from HKLM\SOFTWARE\Siemens\Automation\Networks\ComponentTable. If the OS Client SCE lists an IE General, it is because the runtime PC has the SIMATIC NET driver installed and the Windows NIC is auto-detected – the SCE entry itself is harmless. The fault is the HW Config PC Station, not the driver. Removing the PC Station from the ES-side HW Config of the OS Client eliminates the SDB compile attempt and resolves the NCM diagnostic.

9. Related Error Messages and Diagnostics

The following table catalogues the typical message strings and their correct interpretation. None of these messages should be searched for in the OS Client project once the PC Station has been removed.

10. Step-by-Step Resolution Procedure

The remediation assumes a single-station ES / OS-Server / OS-Client architecture with one OS Server and one OS Client named OSC13, PCS 7 V9.0 SP2 or V9.1. The procedure is captured in the PCS 7 Compendium Part A.

1. Open the multiproject in SIMATIC Manager (or TIA Portal with PCS 7 V17 plug-in).
2. In the project tree, locate OSC13. If it has a child object of type PC Station, delete it.
3. In HW Config of the OS Server, confirm the IE General is present and the SDB compiles cleanly (status bar reads SDB OK).
4. Open the OS Server project in WinCC Explorer. From OS → Target system → Load path, set the path to the OS Server share (e.g. \\OS-Server1\WinCCProj\OS_Server1\).
5. Run OS → Target system → Configure. Verify the success message in the log.
6. On the OS Server, export the server package: OS → Server Data → Export to a network share.
7. On the OS Client PC, import the package: OS → Server Data → Import and confirm the dialog lists the new package.
8. Set the OS Client's path to target computer (\\OSC13\WinCCProj\OSC13\) and click Load. The load log should now end with OS loading successful and no Cannot access target computer line.
9. Open the OS Client's Computer object and check Check computer name – this is the action that resolved the residual "StationManager(index 125) unreachable" message in the field report.
10. Start OS Runtime on the OS Client. Confirm the project picture is shown and the connections to the OS Server appear in the diagnostics.

11. Verification and Commissioning

After applying the fix, validate the system with the following commissioning checks, all of which are documented in the PCS 7 Compendium Part F.

• WinCC Loader log: terminates with OS loading successful and no Warning / Cancel lines.
• NCM diagnostic viewer: OS Server IE General reports SDB OK; OS Client does not appear in the NCM list because it has no PC Station.
• Station Configuration Editor on the OS Client: WinCC Application is RUN, Station Manager is RUN, no IE General listed.
• WinCC diagnostics (ApDiag, Channel Diagnosis): S7 channel of OS Server reports Connected to the AS; the OS Client reports Server connected for the named OS Server.
• Alarm and Tag test: trigger a process alarm in the AS, confirm it surfaces on the OS Server and that the OS Client displays the same alarm within the configured Update cycle (default 1 s for PCS 7 V9.x).
• Redundancy check (if used): confirm WinCC server redundancy partner behaves identically and that the OS Client switches within 1 – 5 s.

12. Preventive Configuration Checklist

The following checklist is used in field commissioning to prevent recurrence.

• OS Client nodes are inserted via Insert OS → OS Client, never as PC Station objects.
• OS Server PC Station has exactly one IE General (or one CP 1623 / CP 1628) bound to the terminal bus.
• The IE General IP / MAC is unique per node and matches the network adapter physically attached to the terminal bus.
• The Station Manager service (S7OMWindows Service) is set to Automatic (Delayed Start) on every OS node.
• Server packages are regenerated and re-imported after every ES-side change to the OS Server's assigned AS connections or picture tree.
• The OS Client load path is a UNC share (not a mapped drive) so that the WinCC loader running under the engineering account can authenticate.
• Windows firewall on the OS Server and OS Client allows TCP/UDP ports used by S7 communication (102, 161, 34964, 49152 – 65535) and by Station Manager.
• SIMATIC NET PC Software version on the OS Client matches the PCS 7 version (V9.0 SP2 / V9.1 / V9.1 SP1) – mismatched SIMATIC NET versions are a known cause of StationManager(index 125) unreachable.