Glad I found this thread as I am having the same problem, on a PC with vista -home installed I can not save to GPX files or convert a GBD file to GPS as in both cases mapsource crashes. Version 6.15.6 of mapsource.
However I have no problems on a Windows XP machine with the same version of mapsource.
Can anyone else confirm if they are having this issue on Vista and not XP ?