I saw this is my debug output:
A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll
So I switched on 'thrown' in exceptions in the debugger and found the missing file to be AvalonDock.Luna. Have you recently switched theme in Windows XP to the silver style? I think that's why AvalonDock is being asked for it's Luna version - which
I don't think exists.