The quiz problems we've seen since last Thursday seem to have been solved. Blackboard restarted 2 of our app servers today and that seems to have done the trick. You should no longer be seeing the HTTP Status 500 error messages or just a white screen when clicking on a quiz to take it. If you are still experiencing any problems with quizzes, please let me know.
Those of you that have been seeing the red "show course" error message in the My Tasks module on the Welcome page can possibly fix this error by going into any course. In the Control Panel expand Customization then click Style. Don't make any changes, but do click Submit to get Blackboard to reread the settings on this page. Hopefully your error message will be gone. If this doesn't work for you, please let me know.