e-file error 601ERRV:4, CustHdr_5.0 ?:? - Invalid Primary SSN

Hi -
When trying to e-file, I am facing error message 601ERRV:4, CustHdr_5.0 ?:? - Invalid Primary SSN
I have cross-checked and my SSN number is correct on forms.
Has anyone else faced the same error?
Can you help.

I am looking forward avoiding a paper filling.

Thanks,
B.