The IRS doesn't require a full middle name.

Exactly what does the reject notice 'say'?

Any chance you're dealing with a hyphenated last name?

And, please don't shout, 'kay?

Sounds like maybe the IRS has their middle name as their last name....IRS only cross matches the first 4 letters of their last name with their SSN/ITIN. 

Many times people with multiple middle or multiple last names, IRS has a different name as "last" in their records.

Do you have a copy of the prior year return to see how it was filed. If that was accepted it should give you a clue what's wrong. Does sound like a it might be part of the last name.