RDCMan v3.21 crashing

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.