Course tracked with number of slides viewed

Hi

I've developed a course in Studio '13.

In the course there are 4 quizmaker files for case studies.

The course is set to Number of slide viewed (30/39).

I've set the tracking to "incomplete/completed".

After publishing and testing the course, the result is that I get the message on the LMS "completed" but "failed".

In the imsmanifest there is the following information. I've never set any masteryscore as the course does not have a final assessment:

 <item identifier="D._Lgs._8_Giugno_2001_n._231_SCO" isvisible="true" identifierref="__5b6GiQ3fmWC_course_id_RES">
        <title>D. Lgs. 8 Giugno 2001 n. 231</title>
        <adlcp:masteryscore>80</adlcp:masteryscore>
      </item>

What could be the problem?

Thanks