".PDB files cannot be linked due to incompatible versions"

The message ".PDB files cannot be linked due to incompatible versions" can be displayed during builds, even if the .PDB file has just been created by the current compilation (ie, its just not possible that it was built by a different version of the compiler)

The problem is that the mspdbsrv.exe process (which Microsoft uses to create PDB files) does not always terminate after linking.  If you have a mixed environment where you compile and link some modules with VC7.0 and then some with VC8.0, sometimes the 8.0 mspdbsrv.exe process hangs around and interferes with subsequent 7.0 compiles.

Solution: use the Task Manager to terminate it.