That could be sourced from any number of working files the quiz module uses. Suggest you go to Site Admin > Development > Debugging and set error messages to "ALL:...". The try again, when the error comes up, it will be logged so find the log and then let us know what it actually says. To me, it looks like there is a double up of a delimiter in a command of some description being written to a page. This could be javascript or php or html... so finding the command will let us know what the issue is.
Also, your theme, what is it?