I have tried many times.
And it came out:
I apologize for this issue. We have worked on this problem and put the fix in production this morning.
I see you are online now, and you are probably still on the VM with this issue. When you have the chance, please stay off the system for about 20 minutes. The system will assign you another VM when you come back and the issue will be fixed. You can then re-attempt the quiz submission.