You're welcome ???

I had one last weekend....the client was ADAMANT he didn't muck things up while trying to get his stimulus check.  Upon further review (it is Sunday & football is on...) he checked back on the IRS website and discovered, low & behold, he HAD filed a $ 1 return.   You might have your client check the IRS website (if they'll admit they did do something/anything vis a vis the stimulus mess), because the *good* news would be that's the problem instead of identity theft.

Hopefully, your client is local so a paper file isn't a big deal.  Mine wasn't, so it got a bit complicated.

Good luck, and let us know what caused the problem in case it IS something else that none of us have seen before.  

Just a thought, HAVE you tried efiling it a couple of times?  Sometimes there are gremlins, especially if you have any PDF's attached.  I did have one last year that I got that reject, tried efiling a couple more times & then it went thru.  NO clue why...the return did have a large PDF attachment.