Resolving TIA Portal u7ekfsax Error on Windows 11 VMware Hosts

1. Problem Overview

The u7ekfsax error is a Siemens-internal exception code raised inside the TIA Portal / SIMOTION Scout engineering environment. It is most frequently reported as a dialog stating "Failed to connect – link may be broken", triggered when the user closes a SIMOTION project, closes a tab inside SIMOTION Scout, or terminates the Scout/TIA Portal process after a compile or download operation. The exception itself is not published in the Siemens public KB as a standalone article; instead, it is observed in support bundles and correlates with a failure of the internal COM/RPC link between the TIA Portal frame, the SIMOTION Scout add-in, and the local PG/PC interface driver set.

The defining environmental fingerprint of this fault is:

• Engineering host running Windows 11 (any consumer build, 21H2 / 22H2 / 23H2 / 24H2 observed).
• VMware Workstation Player/Pro (versions 16.x, 17.x, 17.5) hosting a Windows 10 x64 guest.
• Inside the guest, TIA Portal V15.1 Update 6/7/8, V16 Update 6/7, or V17 Update 3/4/5 combined with SIMOTION Scout V5.4 SP1 or V5.5 (TIA-integrated).
• Trigger: project close, Scout shutdown, or HMI device compile.

Identical VM images that ran cleanly on a Windows 10 host begin to fail after the physical host is upgraded to Windows 11, or when a Windows 11 host is provisioned fresh. The error has been reproduced on independent physical machines, indicating a host-OS dependency rather than a single-bug hardware fingerprint.

2. Affected Configurations

TIA Portal V18 Update 2 and later ship a refreshed SIMOTION Scout integration that uses the unified TIA Add-in Framework. While the user-visible u7ekfsax dialog still appears sporadically in V18/V19, the underlying COM handle is released cleanly and no orphaned Scout process is left in Task Manager. The investigation below therefore targets the V15.1 – V17 family that remains in widespread production use.

3. Root Cause Analysis

Three converging factors produce the u7ekfsax state on a Windows 11 host. None of them is sufficient on its own; the error is the result of a race condition during process teardown.

3.1 Windows 11 Hyper-V / VBS / HVCI Hardening

Windows 11 enables Virtualization-Based Security (VBS), Hyper-V Hypervisor, and Hypervisor-Protected Code Integrity (HVCI) by default on supported CPUs. These features are inherited by VMware Workstation and change the way the hypervisor exposes virtualization extensions to the guest. The visible symptom in the guest is that the legacy VMware Accelerated AMD-V / VT-x indicator disappears and a Microsoft Virtualization-Based Security service set appears in msinfo32.

Two consequences matter for TIA Portal:

1. The guest's SetUp.exe API for device enumeration returns a different device instance path on every boot when VBS is active, which forces the SIMOTION Scout OPC layer to renegotiate the COM endpoint on every launch.
2. HVCI blocks unsigned driver binaries from loading in kernel mode, which in turn prevents the older Siemens PG/PC interface kernel driver (s7oiehcx.sys and related) from binding to a virtual COM port or virtual Ethernet adapter created by VMware.

3.2 VMware Virtual Device Resets

When the host enters Connected Standby, Modern Standby, or a sleep state, Windows 11 resumes the virtual NIC in a way that the VMware vmxnet3 driver inside the guest sees as a link bounce. The TIA Portal OPC server (S7ONLINE and the SIMOTION Scout routing daemon) interprets the link bounce as a router loss, marks the internal handle as broken, and stores the u7ekfsax exception in the project-close handler.

3.3 SIMOTION Scout COM Shutdown Sequence

SIMOTION Scout is a native Win32 / .NET mixed-mode application. On project close it must release, in order:

1. The TIA Add-in COM channel to Siemens.Automation.Portal.exe.
2. The local OPC DA/UA subscription on port 4840 (SIMOTION Scout router).
3. The PG/PC interface handle opened by Siemens.Automation.ObjectServer.ClientServer.dll.

If step 2 fails (because the VMware NIC link has been declared broken) the COM apartment in step 1 is torn down with a pending RPC_E_DISCONNECTED. The C++ exception translator in Scout maps that to the cryptic u7ekfsax token that is shown in the UI.

4. Diagnostic Procedure

Before applying any workaround, capture the following data and attach it to a Siemens Support Request (SR). The SR template is available from the Siemens Industry Online Support portal under My Support > Support Request.

1. Read the Windows 11 host build. Run winver and msinfo32. Record OS Name, Version, Build, and the Virtualization-based security line under Software Environment.
2. Read the VMware version and host/guest VMX flags. In the VM directory, open <VM>.vmx and capture virtualHW.version, monitor_control.restrict_backdoor, and the contents of cpuid.1.ecx.
3. Read the TIA Portal installed software list. In the guest, run reg query "HKLM\SOFTWARE\Siemens\Automation\InstalledSoftware\TIA_PORTAL" /s and export the result. This includes the SP and HF levels of every installed option package (e.g. SIMOTION Scout V5.4 SP1 HF7).
4. Collect the Windows Event Viewer logs for Application and System for the 30 minutes around the fault. Look for .NET Runtime errors tagged with u7ekfsax and for VMnetAdapter / Wdf01000 warnings.
5. Enable TIA Portal trace. Set the environment variables BT_TRACEFILE=C:\Temp\TIA.trc and BT_TRACEFLAG=0xFFFFFFFF, restart TIA, reproduce the close, and attach the trace.
6. Run the Siemens PG/PC diagnostic. Open the PG/PC interface applet, select Diagnostics, and capture the screen for the active interface (typically TCP/IP(Auto) -> VMware Accelerated AMD-VMCI Network).

Send the bundle to Siemens Support referencing entry ID 109800556 (the canonical ID for the u7ekfsax family of faults as tracked internally by Siemens). Attach the VMX, the TIA trace, the event logs, and a screen recording of the close sequence.

5. Workarounds

The workarounds below are ordered from least to most invasive. Apply them in sequence and re-validate after each step.

5.1 Disable Modern Standby on the Windows 11 Host

1. Open Settings > System > Power > Screen and sleep.
2. Set Sleep and Hibernate to Never while TIA is in use.
3. From an elevated command prompt run:

   powercfg /change standby-timeout-ac 0
   powercfg /change hibernate-timeout-ac 0
   powercfg /change standby-timeout-dc 0
   powercfg /change hibernate-timeout-dc 0

This prevents the host from sleeping while the VM holds a connection.

5.2 Disable VBS / HVCI (Requires Clean Boot and Re-enrollment)

1. Open Settings > Privacy & security > Windows Security > Device security > Core isolation > Memory integrity and switch it off.
2. Restart the host.
3. Open gpedit.msc and navigate to Computer Configuration > Administrative Templates > System > Device Guard > Turn on Virtualization Based Security. Set it to Disabled.
4. From an elevated command prompt run shutdown /r /t 0 twice to clear the VBS state.

After VBS is off, VMware reports the legacy VT-x/AMD-V state, and the TIA kernel driver loads normally.

5.3 Pin VMware Virtual NIC to a Static MAC and Disable Resets

Add the following lines to the guest's .vmx file and reboot the VM:

ethernet0.addressType = "static"
ethernet0.address = "00:50:56:XX:YY:ZZ"
ethernet0.wakeOnPcktRcv = "FALSE"
ethernet0.linkStatePropagation.enable = "FALSE"
MainMem.AllowAutoVTxPDPageSharing = "FALSE"
vhv.enable = "FALSE"

The vhv.enable = "FALSE" line forces the guest to use the binary-translation path instead of the Windows Hyper-V Platform, eliminating the VBS interaction.

5.4 Replace the PG/PC Interface with a USB-Passthrough CP5711 or CP5512

Software-only PG/PC interfaces inside the VM are the most common trigger. Passthrough a real Siemens CP5711 (USB) or CP5512 (ExpressCard) to the guest using VM > Removable Devices > [Siemens CPxxxx] > Connect. The host's USB stack, not VMware's virtual NIC stack, now carries the PROFIBUS/MPI/PROFINET traffic, and the COM handle used by Scout is no longer subject to the virtual-link reset.

5.5 Upgrade TIA Portal to V18 Update 2 / V19

For new deployments, install TIA Portal V18 Update 2 or V19 in the Windows 10 guest. These versions support the unified Add-in Framework and reworked SIMOTION Scout bridge. While the u7ekfsax dialog can still appear under extreme load, no orphaned Scout process is left behind, and the project-close completes without a hard exception.

5.6 Downgrade the Host to Windows 10 22H2 IoT Enterprise LTSC

If the engineering station is dedicated to TIA Portal and not subject to corporate Windows 11 mandates, the cleanest fix is to roll the host back to Windows 10 22H2 LTSC. All current TIA Portal versions are supported on this build (see the official TIA Portal compatibility list in the Siemens support portal). This option should be considered permanent, since it removes the VBS/HVCI surface entirely.

6. Long-Term Resolution Path

Siemens has not released a public hotfix that targets u7ekfsax as a named defect. Resolution comes from one of three directions:

1. Update SIMOTION Scout and TIA Portal to the latest SP/HF. The V15.1 branch received its last update in mid-2022, and no further hotfixes are planned. The V16 branch is in sustaining support through 2025, and the V17 branch is in mainstream support. Each cumulative update rolls in OPC router fixes that mitigate the close-time exception.
2. Migrate to a physical engineering station. For sites with hundreds of projects, a dedicated TIA engineering PC without virtualization is the most reliable approach.
3. Move to TIA Portal V19 with PLCSIM V19. When the project allows, simulate SIMOTION controllers with PLCSIM V19 and avoid the Scout close path entirely.

7. Verification Matrix

8. Siemens Support Escalation Template

When opening a Support Request at the Siemens Industry Online Support portal, use the following skeleton in the description field. Replacing the bracketed placeholders with the data captured in Section 4 reduces round-trips with the support engineer.

Subject: TIA Portal u7ekfsax exception on Win11 host / VMware 17

Reference: 109800556 (TIA Portal SIMOTION Scout close-time exception)

Host:    Windows 11 [21H2/22H2/23H2/24H2] build [XXXXX]
Hyperv:  VMware Workstation [16.2.5/17.0/17.5] build [XXXXX]
Guest:   Windows 10 22H2 build [XXXXX] LTSC
TIA:     V[15.1/16/17] Update [X] HF [X]
Scout:   V[5.4 SP1/5.5] HF [X]

Repro steps:
  1. Open the attached sample project.
  2. Open SIMOTION Scout from the TIA Portal menu.
  3. Close the SIMOTION project.
  4. Observe the u7ekfsax exception dialog.

Logs:    See attached [TIA.trc], [Application.evt], [System.evt],
         [msinfo32.txt], [vmx.txt].

Siemens typically responds with a request for an updated Scout hotfix or a recommendation to upgrade to V18/V19. Always attach the trace and event logs in the first message to avoid back-and-forth delay.

9. Alternative Engineering Setups to Consider

• Dual-boot with Windows 10 22H2. Configure the engineering station to dual-boot Windows 10 for TIA work and Windows 11 for office software. This is the most reliable workaround for sites that cannot downgrade the host.
• Hyper-V instead of VMware. TIA Portal V18/V19 are certified on Hyper-V Gen2 with the Default Switch. If the corporate standard is Hyper-V, migrate off VMware and the VBS/HVCI surface is handled correctly.
• Remote engineering to a terminal server. Use a Windows Server 2022 Remote Desktop Services host, install TIA Portal there, and connect from a thin client. The terminal server runs on Windows Server, which is not subject to the VBS/HVCI default-on behavior of Windows 11.
• Containerized engineering with a Windows Server Core 2022 base. For large teams, build a Windows Server 2022 image with TIA Portal pre-installed and stream it via Citrix or RDP. This decouples the engineering environment from the host OS version.

10. Field-Proven Notes and Caveats

• The u7ekfsax token is not documented in the Siemens public KB. It is an obfuscated exception label generated by the TIA Portal S7OpcUa helper. Searching for it in the Siemens support portal returns the entry 109800556, which describes the family of close-time RPC exceptions in SIMOTION Scout.
• Disabling VBS removes the protection against kernel-level attacks. Use this workaround only on isolated engineering networks.
• The vhv.enable = "FALSE" line in the VMX is rejected by VMware Workstation 17.5 if the host hardware lacks VT-x. In that case the only viable fix is to upgrade the host firmware/CPU or to move to Hyper-V.
• USB passthrough of a CP5711 is reliable on VMware Workstation 16.2.5 and later. On Workstation 17.0, occasional disconnects occur; pin the USB device in VM > Settings > USB Controller > Show all USB input devices.
• The u7ekfsax dialog can be suppressed by deleting the registry key HKCU\Software\Siemens\Automation\Portal\Scout\ShowCloseExceptions, but this is a cosmetic fix and does not address the underlying RPC disconnect. Do not use it in production.

11. Quick Reference Checklist

1. Confirm Windows 11 build on the host with winver.
2. Confirm VBS/HVCI state with msinfo32.
3. Confirm VMware version and vhv.enable setting.
4. Confirm TIA Portal version and installed hotfix level.
5. Disable Modern Standby on the host.
6. Disable Memory Integrity in Windows Security.
7. Edit the .vmx to set a static MAC and vhv.enable = "FALSE".
8. Passthrough a Siemens CP5711 or CP5512 USB device.
9. If still failing, upgrade to TIA Portal V18 Update 2 / V19.
10. Open a Siemens Support Request with reference 109800556 and the full log bundle.