It's probably doing that because it's using last years agi along with your ssn, as your "electronic" signature. If your agi doesn't match up from last year, it will kick your return. If worse comes to worse, you might be able to just print the sig page and mail it in, in lieu of the electronic sig. Usually that does the trick.
Also, there are lots of programs that let you efile for free. I've done about 30 tax returns in the last month so I'm ready to puke from it, but take a look at this page:
http://www.irs.gov/efile/
Be sure to check out this page, also. I think it has most of the free file programs:
http://www.irs.gov/app/freeFile/jsp/index.jsp?