Visual Studio will create ‘obj’ folders within your solution to store a bunch of temporary files. You can remove these files in a number of ways.
One easy way is to use Windows 7 Search to look for all the ‘obj’ folders and just delete them manually.
To do this I use the ‘kind’ keyword in the query box.
Tip: Just typing ‘kind:’ will give you a list of choices to choose from.
For a complete overview of the Windows 7 Search syntax go to: http://www.microsoft.com/windows/products/winfamily/desktopsearch/technicalresources/advquery.mspx