I am using Moodle 2.0. My students have been getting the above error when they try and submit a quiz with an essay question in it. After a little experimentation, it appears that the error shows up only when they have hit 'enter' to move to the next line inside of the essay response box, and then it only shows up when they try and submit the quiz. Is there anyway to fix this?
Presumably random questions are involved somewhere, or you would not be getting that error message?
Yes...the questions giving the error are random essay questions. It appears to only happen when using the TinyMCE editor. I switched to the plain text editor and haven't seen the error yet. This is a bit of a problem, as you lose any sort of easy formatting capabilities.
I can reproduce this, so I reported it to the bug tracker: MDL-26236.