Snow Leopard, Active Directory : cannot save a file, but 'save as' is working
I found a workaround to the problem :

The path to the document was the following :

smb://srv-fichiers1/Personnel/myhome/mydoc.txt


The problem was that I didn't have read/write access to the Personnel folder.

The administrator added read/write access to this folder and now, everything is working fine.

I agree that this is more a workaround than a real solution, but it does the trick for me !