At my company, we use SourceSafe 2005 for source control.  It allows administrators to configure it to have one of the following check-out models:

• Exclusive Check-Out Model: Lock-Modify-Unlock mode that only allows one user to modify a resource at a time.
• Multiple Check-Out Model: Copy-Modify-Merge mode that allows multiple users to modify a resource at a time, after which a merge operation is performed at which point any conflicts between the changes can be addressed and resolved.  In my experience, the merge can typically be done automatically without any issues.

Although we usually only have two people working in the project at a time, there are still times when it would be convenient to allow both users to modify different sections of the file at the same time.  However, the few times we have done that one of the developers gets an error message the next time they try to build the solution that says "Access to the path _ is denied."  We didn't notice that this was the file that required the merge for a while, but finally pinpointed that to be the problem.

I found a blog post that explained the issue.  It turns out the "Include inheritable permissions from this object's parent" property of the merge files had been cleared.  If you simply re-check this property, the solution should build properly.  This is just seems to be a bug with the merge functionality in SourceSafe, and will hopefully be something they fix in the future.