The build cannot be assigned to the test plan

One of the customer reported a problem saying that whenever he is trying to assign a build to the test plan in MTM, the assignment fails with error “Build XXX cannot be found”. 

On investigations, Nipun from the team found that it was failing because the customer was not using the default permissions and the account under which the team foundation server is running did not have permission to query the build.  On granting that permission, it started working.