If you haven't already, run through the complete calibration/adjustment procedure. The 3314A attempts to correct itself, but it can only adjust its parameters over a short range and it assumes they are close to begin with.
My 3314A will often throw a Error 31 (frequency error exceeds correction capability). I can usually get rid of that error by following the frequency accuracy calibration adjustment described in section 5.9 (at least, that's the section number in my version of the service manual).