Error "the filename was already in the collection" on rebuild

Hi,

       We am having the following error when we are re-building a project.

Error 61 The file name 'C:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\pipp\52edbab2\4a4d23bd\vi43v4nx.pdb' was already in the collection. Parameter name: fileName

We tried a number of things from deleting the "Temporary ASP.NET Files", installing service packs, updates, deleting other temp directories etc. We are not even trying to debug the project. Just trying to rebuild the project is giving the error. 

Any help is greatly appreciated.