The selected problem set (name of test) is not a valid set for (me). One or more of the problems in this set have not been assigned to you.
Right now the quiz is set to be invisible and it's been assigned to myself only. I thought that's the issue, until I export this quiz, and then reimport it under a new name --- so the duplicate has the identical settings (invisible to everyone etc). BUT: I can take this new version!
So what's going on, what settings should I change to make this error message goes away? And how can I test things out so that I can be sure it will work when I give the test? --- I created a separate test account and everything worked there before I moved the files to the actual account, so I'm baffled (and panicking...) Thanks for your help!