I don't know the real issue, but I can remember a couple of instances in prior years where there was an issue with a form and they held those returns for a bit until they fixed the issue.  When they got the issue fixed, the returns were rejected so that they could be re-transmitted with the corrected version of the form.  But like I said, I don't know if that is what is going on or if they have other issues mucking up the system.