The briefcase works off of a database that tracks files and changes to those
files. If this database becomes corrupted, then you will lose access to your
briefcase. I had this problem when I tried to use it to sync 80GB of
important files (it apparently isn't designed to handle that. I ended up
splitting it up into multiple folders and it's handling 20+ GB pretty well,
although access is slow). If you simply cannot get into the briefcase, then
there's no way to disconnect it from the original, and you're SOL... Time to
delete the briefcase and start over.
Now, if your access problem is not when you double click on the briefcase,
but when you right click on a file and choose "send to briefcase" you are
still in the game. This is simply a case of mistaken identity, windows has
forgotten where the briefcase is and you need to tell it. Follow the
instructions here to fix this problem:
http://support.microsoft.com/support/kb/articles/Q129/2/57.asp
Hope this gets you on the road to recovery, gents.