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azavalaVP's avatar
azavalaVP
Copper Contributor
Sep 02, 2026

RDCMan v3.21 crashing

Getting the following error

System.NullReferenceException: Object reference not set to an instance of an object.

at RDCMan.Nodes.Server.Dock()

at RdcMan.ServerForm.OnClosed(EventArgs e)

at System.Windows.Forms.Form.WmClose(Message& m)

at System.Windows.Forms.Form.WndProc(Message& m)

at RdcMan.RdcBaseForm.WndProc(Message& m)

at System.Windows.Forms.NativeWindow.Callback(HWND hWnd, UInt32 msg, WPARAM wparam, LPARAM lparam)

The error seems to happen when I have an undocked session, I restart the remote machine on the the undocked window, and it stays open, when I try to reconnect, on the same undocked window, it opens another docked session, I can login to the new session, and undock it, so now I have two undocked windows, the old one (disconnected) and the new one. I try to close the old one and I get the error shown below, (details above). If I click Continue, nothing happens, if I hit Quit, it closes RDCMan, as stated in the window.

 

BUG

2 Replies

  • Jamony's avatar
    Jamony
    MCT
    Sep 03, 2026

    You isolated a repeatable RDCMan 3.21 failure: an undocked session survives a remote reboot, reconnecting creates a second window, and closing the stale window throws NullReferenceException in Server.Dock. That sequence points to broken window/session state rather than RDP authentication. Back up the RDG file and its automatic .old copy. Start RDCMan with /noopen, create a new group with one server, and repeat reboot, reconnect, undock, and close. If the new file works, rebuild or selectively import the original groups. If it also crashes, close RDCMan and test once with /reset to clear persisted preferences. Avoid choosing Continue because the failed state remains loaded. If a clean RDG and reset still reproduce the crash on 3.21, submit the stack trace, RDG topology, Windows build, and minimal reproduction through Sysinternals feedback. That combination would indicate a product defect requiring a Microsoft fix.

  • hmakhlouf's avatar
    hmakhlouf
    Copper Contributor
    Sep 02, 2026

    That's a bug in RDCMan, not something you've misconfigured nothing on your side will fix it.

     

    Workarounds in the meantime : Dock the session before rebooting the remote host, so no orphaned undocked window exists when it comes back. bu If it's already orphaned, close the stale undocked window first, then reconnect from the tree. The crash needs two live windows bound to the same server. and finally Use the Reconnect command on the node rather than clicking inside the dead undocked window, so RDCMan reuses the existing session instead of spawning a docked one.

     

    And save your .rdg before you experiment, since Quit is your only exit from that dialog.