When a user tries to send a test response, the error message “We’re sorry, there was an error with processing your request. Please try reloading your page and trying again.”
This indicates that there’s an error on the server. It could be a temporary issue, or it could be something more severe. You’ll have to locate the real error in the logs, which requires access to your server.
For single server Open edX instances, I do this by shelling into my server and running the following command:
sudo tail -f /edx/var/log/**/*.log
Then watch the output while reproducing the issue.