I had the same thing on an 8-31 year end (Due Yesterday). I kept checking and got the same (I think) rejection, so opened the file, ran error checking again, saved and resent.

Then I took the Extension that was on my desk, and went to the PO and mailed, certified, return receipt requested. (I know you are supposed to be ok if you have to fix something on a reject, but it is easier not to take chances.)

As of this morning the return is still sitting in "Sent to IRS Status" but with the extension if there is a systemic problem that takes a while to get fixed, I don't have to worry (as much).