If the residuals test fails, check the results of the DANL TEST. If DANL is out of spec, there is a good possibility that the high average noise level is causing the residuals test to indicate a false failure.
Also assure the 50 ohm load is attached to the MXE RF Input connector. Failures are usually caused by loose or defective cables or loose shielding on an assembly. See the MXE Service Guide for troubleshooting information.