Lacerte/Intuit can't help.  The IRS has already received a tax return using your client's SSN.  Nothing can change that fact, especially with 4.5 days to go.

As Susan said, it is caused by either:

1) Your client (despite what they may claim....) clicked on the wrong thing when trying to get their stimulus check and filed a return (usually, showing $1 in interest income).

If this is the case, you *could* file an amended/superceding return... but.... wait for it... you can't efile an amended return unless the original return was filed using Lacerte.

2) A legit mistake somewhere along the way by someone filing but using your client's SSN (transposition error, etc)  - it does happen.

3) Identity theft.

The ONLY option is to paper file. 

And you should advise your client to ASAP monitor/check banking & credit card activity to see if it IS identity theft.  If it is, the IRS will get involved & your client will be issued a number to enter for future efiling purposes.