questions do not appear in quiz take ("no questions found. please assign questions..")

Hi,
I have some trouble with quiz module. I am using Quiz, "Quiz Questions" and "Quiz Multichoice". (When I refer to question below, I mean multiple choice questions.)

On some older quizes on my drupal site I get no questions in the "take"-section although there are question in the "manage questions"-sections. Also when I add a new question to the quiz it does not appear in "take". Instead I get this message on take: "No questions were found. Please assign questions before trying to take this Quiz."

In the logs I get these notices after I tried to take a quiz:
Notice: Trying to get property of non-object in quiz_quiz_finished() (Zeile 2332 von /../sites/all/modules/quiz/quiz.module).
and
Notice: Undefined index: quiz_ in quiz_take_quiz() (Zeile 2043 von /../sites/all/modules/quiz/quiz.module).

I have searched trough the quiz related database tables. The link between the quiz and the multiple choice questions in the quiz_node_realtionship table seems to be set correctly. Also when I add or remove a question through "manage questions" there where made revisions in this table.

In some cases also the "questions in this quiz"-sections is empty resp. remains empty when I add a question although there are relations in the node_relationship table and although the added question disappear in "browse for questions to add"-section.

In contrast to this behavoir adding a new quiz and assigning some questions to it works fine.

Can anyone help or has similar problems?

Thanks, mirkba