I got this funky error after just making a small change to a file.

Error ## The item “xxx” was specified more than once in the “Resources” parameter. Duplicate items are not supported by the “Resources” parameter

Build->Clean doesn’t fix it. If you encounter this same error, try the following.

Open your vbproj file in a text editor. If your project is called “myProj”, then the file name is “myProj.vbproj”. (Make a backup first…)

Then search for “EmbeddedResource”. You will see something like the following:

      Designer
      MyGreatFrm.cs

Then search for the troublemaker “xxx”. You will likely see duplicates. Use your discretion to delete the bad ones.

Then save it, you are done. VS.NET will force you to reload your project.

Thanks to miche1024 at this post: http://social.msdn.microsoft.com/Forums/en-US/msbuild/thread/df3bee5f-8081-4425-aca7-70bfbc15fb30