Resolving S7-PLCSIM 'Application is Currently Being Used' Lockout Without Rebooting Windows

When S7-PLCSIM fails to open and displays the error message 'This application is currently being used' following a software crash in SIMATIC PCS 7 V8.1, the issue is caused by orphaned background processes retaining exclusive memory locks. You do not need to restart the Windows operating system. To resolve this, open Windows Task Manager, switch to the 'Details' or 'Processes' tab, and terminate the orphaned background tasks 's7wpa01x.exe' (PLCSIM core engine) and 's7wndsrv.exe'. Once terminated, relaunch S7-PLCSIM from SIMATIC Manager.

Executive Summary

Simulation is an indispensable phase of DCS engineering. When testing automation logic in SIMATIC PCS 7 V8.1 running inside VMware virtual machines on Windows 7 SP1 (64-bit), unexpected crashes in CFC, STEP 7, or third-party tools can cause the engineering interface to close abruptly. However, underlying simulation daemons frequently remain running in the background. When an engineer attempts to restart S7-PLCSIM, the operating system blocks initialization with: 'This application is currently being used'. Many engineers resort to lengthy operating system reboots. This guide details the process architecture of S7-PLCSIM and provides instant process termination routines.

Architectural and System Mechanics

S7-PLCSIM Process and Memory Architecture:

Multi-Process Service Model: S7-PLCSIM is not a monolithic application; it consists of several cooperating executables:
s7wpa01x.exe: The primary simulation runtime kernel that emulates S7-400 CPU memory, cycle timers, and communication buffers.
s7wndsrv.exe: The window server interface managing GUI interactions and variable views.
s7ussrva.exe: The user interface server bridging STEP 7 COM calls to the virtual CPU.
Mutex and Shared Memory Locks: During startup, s7wpa01x.exe creates a named Windows mutex and allocates shared memory segments. If the GUI crashes while s7wpa01x.exe is alive, the mutex remains locked. Subsequent launch attempts detect the existing mutex and abort with the 'application in use' dialog.
Compatibility Matrix: In PCS 7 V8.1, S7-PLCSIM V5.4 SP5 is certified for Windows 7 Professional/Enterprise SP1 (64-bit). Ensure all PCS 7 V8.1 Service Pack 1 updates are installed.

Step-by-Step Engineering and Implementation Procedure

Step 1: Terminate Orphaned Processes via Windows Task Manager

Press Ctrl + Shift + Esc to open Windows Task Manager.
Switch to the Details tab (Windows 10/Server) or Processes tab (Windows 7).
Locate and select the following executable processes:
- s7wpa01x.exe
- s7wndsrv.exe
- s7ussrva.exe
Click End Task (or End Process) to forcefully terminate them.

Step 2: Instant Process Kill via PowerShell / Command Prompt

To terminate all simulation daemons instantly without navigating Task Manager:
1. Open Command Prompt or PowerShell as administrator.
2. Execute the following command:
cmd taskkill /F /IM s7wpa01x.exe /IM s7wndsrv.exe /IM s7ussrva.exe /T
3. The terminal confirms: SUCCESS: The process with PID ... has been terminated.

Step 3: Clear Temporary Simulation Files

Navigate to the Windows temporary directory (%TEMP%).
Delete temporary files starting with s7* or .sim files if simulation project states were corrupted during the crash.

Step 4: Relaunch S7-PLCSIM from SIMATIC Manager

In SIMATIC Manager, click the Simulation On/Off icon in the toolbar.
Confirm that S7-PLCSIM initializes cleanly with a fresh virtual CPU window.

Verification

To verify proper simulation operation:
1. In the S7-PLCSIM window, set the CPU mode switch to 'RUN-P'.
2. In SIMATIC Manager, open HW Config and download the hardware configuration to PLCSIM.
3. Open CFC, execute a test chart download, and activate test mode (Ctrl + T).
4. Verify that live values update dynamically in the CFC sheet.

Limitations and Operational Precautions

Operational precautions:
- Forcefully terminating s7wpa01x.exe while a download is active may leave the virtual CPU memory file (*.plc) in an inconsistent state; always reload HW Config and AS program after terminating orphaned processes.
- Never run S7-PLCSIM on a production engineering station physically connected to a live plant bus unless the PG/PC interface is strictly set to PLCSIM(MPI) or PLCSIM(ISO), preventing accidental simulation packets from reaching physical controllers.
- Verify VMware virtual machine resources: allocate at least 2 dedicated vCPUs to prevent CPU starvation between SIMATIC Manager and PLCSIM.

Engineer FAQ

Q: Why does PLCSIM say 'This application is currently being used'?

A: Because the background simulation engine process s7wpa01x.exe remained running after an interface crash, holding the application lock.

Q: What is the primary process name for S7-PLCSIM?

A: The core process is s7wpa01x.exe.

Q: Do I need to reboot Windows when this happens?

A: No. Terminating s7wpa01x.exe and s7wndsrv.exe via Task Manager or taskkill immediately clears the lock.

Q: Can PLCSIM simulate redundant S7-400H controllers?

A: Standard S7-PLCSIM V5.4 simulates a single CPU. For redundant H-controller simulation with automatic switchover, SIMIT Simulation Platform or PLCSIM Advanced (for S7-1500) is required.

Q: Where can I verify software compatibility for PCS 7 V8.1?

A: Consult the official Siemens Kompatool (Compatibility Tool) on SIOS.

Technical References

Related Tags

S7-PLCSIM, s7wpa01x.exe, Taskkill, Simulation Crash, PCS 7 V8.1

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Resolving S7-PLCSIM 'Application is Currently Being Used' Lockout Without Rebooting Windows