I once had a similar problem with source safe in VB 6.0 At least I saved all files of the project ( in the actual version ! ) in another directory. There I made all files writeable again. Then I deleted the project in the source safe and in the old directory too. Then I copied the files back from the directory where I had saved them into the original directory and loked if they are still all writeable. They was. Then I started VB and safed the project in VSS again.
Then all worked as it should.

IMHO in my case Source safe and the program wasn't synchron regarding which files are writeprotected (probelms because this code was asynchron to VSS before SP 6 and stayed in that condition after installing SP6 ) and which not and this brought all my troubles.

I hope your troubles are similar and this will help you

Jonny Poet