It sounds like a glitch on our part. To submit the assignment, it must be completed so if you haven't finished the assignment that might be why it isn't submitting. Check to make sure you have completed the entire assignment.
If you have finished the assignment and it still isn't working it's definitely a glitch that we would like to fix. Please email email@example.com and we will be sure to report the bug and follow-up with you to get it fixed.