Could start by turning on debugging all the way to developer level, then do what you did to get the 'popup'? undefined error box?
Then come back here and post whatever that said.
If you are an admin, run hidden health tool:
https://site/admin/tool/health/
Do that in non-prime time ... health check might be pretty intensive.
One of the things health check does is check on quizzes. If it finds issues ... provides a small chart of quizzes involved and also provide a 'See Solutions' button.
The text of that chart you could share back here.
Solution, if there is one, is usually an SQL query that you could run via PHPMySQL or mysql client from cli.
'SoS', Ken