A disregarded entity of a LLC would not always be a xx-xxxxxxx format. In many cases the DE is an individual and should be entered as xxx-xx-xxxx. I believe this is a software error as several days ago this entry was NOT flagged as an error. It just showed up today (not yesterday) for me
Well, I went ahead and entered the individual's SSN in the XX-XXXXXXX format and the error went away. Not great software as it should allow a DE TIN in either format as the DE can be a Trust or an individual; each with a different format.