To solve this problem you have to clean the cache folder on your machine.

  1. Press Win + R together to open the Run window

  2. Type in %UserProfile%\AppData\Local and click on **OK

    **

  3. Navigate to the Microsoft\Team Foundation\6.0\Cache folder and delete all contents

  4. Restart Visual Studio and Re-Open your solution.

  5. The error message will disappear and all should be working again.