This error indicates that service revisions did not run completely and successfully. To rerun service revisions:
  1. Navigate to C:/Program Files/Blackbaud/bbappfx/MSBuild
  2. Double click the bbAppFx.Config to begin running the application
  3. Select RunServiceRevisions on the left hand side
  4. Click Go to "Execute the "RunServiceRevisions task" 
Once service revisions complete successfully, the testconfig.aspx page should now load.