...
Rule Text: For the filing status selected in the return, the Primary SSN in the Return Header must not be the same as the Spouse SSN on another return for the same tax year with filing status Married married filing separately.
To correct the error, reference the DataValue (this indicates what person or number the rejection is related to). For more information, regarding how to view the details and data values related to rejections and refusals reference Viewing Reject and Refusals.
...
Possible Cause 1: The taxpayer is married and their spouse filed already filed MFS.
Resolution: If the taxpayer is married they must file as MFS, unless they qualify for HOH status.
...
Possible Cause 2: The taxpayer is a victim of identity theft or preparer error.
Resolution: Collect prep fees upfront and paper file the return along with Form 14039.
...