I began to receive the error message box in Visual Studio after a restart from an install of an unrelated to test Visual Studio plugin (which I have used in the past):

The ‘TestWindowPackage’ package did not load correctly.  … examining the file … AppData\Roaming\Microsoft\VisualStudio\12.0\ActivityLog.xml

Looking at that log showed these errors:

TestWindowPackage.Initialize failed with exception … System.InvalidOperationException:

Loading MEF components failed with the following exception:
The composition produced a single composition error. The root cause is provided below. Review the CompositionException.Errors property for more detailed information.

No exports were found that match the constraint:
    ContractName    Microsoft.VisualStudio.TestWindow.VsHost.PackageContainer
    RequiredTypeIdentity    Microsoft.VisualStudio.TestWindow.VsHost.PackageContainer


To resolve the issue I did step 1 and 2 but am showing step 3 in case it helps.

  1. Close all instances of Visual Studio.
  2. Delete all files in AppData\Local\Microsoft\VisualStudio\12.0\ComponentModelCache Note that directory is not found in Roaming as the activity log file, but in Local.
  3. Restart, if that doesn’t work then start over with step 4.
  4. From a Visual Studio Command Line do this operation: devenv /setup /ResetSkipPkgs See (/Setup (devenv.exe)) for more information.