Ashley-
I'm not familiar with that software, but i have used others like it. The term mismatch is pretty unhelpful. My suggestion though is to think bigger picture. You are really just trying to make sure the applicant has good credit. So work on verifying that the person who is applying to rent is attached to the credit report that you are looking at. Ask the applicant for a divers license and their SS card. Make sure the name and date of birth on the drivers license matches the name on the credit report. A mismatch error could be indicating that the SSN is associated with a different name, date of birth or other identifying information. The systems often make errors, but identity theives are usually very good talkers. So definately take the time to verify the individual.
In a case like this, definately call several previous landlords. Lookup the owner of the previous rentals yourself and find a phone number. if you do get a landlord on the phone, it wouldn't hurt to ask if they had a similar error.