While in Visual Studio you may start seeing temp files start to appear in your solution. You delete them and all of a sudden they reappear again.  In many cases this a problem with your anti-virus solution.  Go into your AV solution and exclude the Visual Studio types from being scanned, especially the *.vb and *.cs extensions.

In my case this happened with Microsoft Security Essentials. I did not have this problem when running Microsoft OneCare or earlier versions of Free AVG. It also seems like this problem surfaces a lot with Trend Micro solutions as well.