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Positioning Application: What causes the warning message "No contact with simulation engine process" OR "Lost contact with Engine" OR "cannot connect to simulation engine"?

  • PosApp (SimGEN / SimREPLAYplus / SimREPLAY) v4-00 or later
  • One of the following pop-up messages is displayed

  • The most likely root cause of the GUI and engine losing connection over Ethernet is due to the PC entering some sort of 'inactive' or 'sleep' state.
    • Either whilst in a "Ready to run" state or during a scenario run
  • This can happen if there has been no human interaction for some time
    • Windows might enable a screen saver, even if applications are running.
    • Equally, most modern PCs have power saving features which will turn off the monitor or even set the PC to 'sleep' / 'hibernate'.
  • Windows Firewall settings may have changed
    • If the firewall is ON check for exceptions for the following programs
      • posapp.exe
      • posapp_engine.exe
  • Windows can close Ethernet port connections that are inactive or perhaps operating at a low level (see NOTES below to learn why this affects the GUI/engine)
  • Therefore, for each PC user account that is used to run PosApp the user should

    1. Ensure PC configuration is in accordance with our standard advice (see DCS0036D for Windows 7, DCS0036B for Windows XP)
    2. Disable the screen saver
    3. Disable or modify power saving rules so that Windows avoids setting the PC into 'sleep' / 'hibernate' mode.
  • If running PosApp for the first time after a version update or a reinstall then try right clicking on the .exe and  select "run as Admin".   This will allow additional files to be written if needed by the system. 


  • The PosApp GUI communicates with the PosApp engine via an Ethernet socket
  • The error message in Figure 1 is displayed when that socket connection is lost.
  • You can choose to
        a) Wait for the GUI to re-establish the connection
        b) Restart the GUI and engine
        c) Close the application altogether
  • Although the GUI may have lost connection with the engine the engine itself may still be running normally in the background
    • Check Windows Task Manager 'Processes' list - does it still show "PosApp_engine.exe" is running?
    • Check to see if the simulator is still running (LCD displays active channels or the ACTIVE LED is illuminated, depending on simulator model).
  • So it can be an advantage to not restart or close the application straight away in order to let the simulation continue to the end.
  • Equally, if the GUI does re-establish connection with the engine the pop-up message will automatically close.
  • Please refer to article FAQ12157 which explains the change made to the software architecture with PosApp  v4-00.



If PosApp GUI / engine disconnections are still experienced after following the above suggestions

  1. Use the "Open a Service Request" link on the right side of the Knowledge Base area to open an enquiry with Spirent Global Services
  2. Confirm the PosApp version (go to menu [Help-->about])
  3. Please send a copy of the "PosApp_message_log.txt" and "PosApp_engine_message_log.txt" files that were captured during a GUI/Engine disconnection
  4. Confirm the Windows OS being used
  5. Confirm that you have followed the above advice regarding the screen saver and power save options


Product : SimREPLAYplus,SimREPLAY,SimGEN,PosApp,Positioning