Restricted navigation problems

Hi all,

I need to restrict navigation on a course and I followed indications as per link below:

http://www.articulate.com/support/kb_article.php?product=st1&id=3nq6s9jfveap

It works fine in the menu, the users cannot jump to a slide forward, anyway I have a strange behaviour.

If I try to go back to review the viewed slides sometimes the next button not Always is working.

Sometimes the course blocks without going forward. Joking a little bit with the previours button or with timeline somehow solves the problem resetting the next button (until the timeline goes to the end) and then it works again.

Sorry it is quite difficult to describe as malfunction...

Does anybody has any suggestion for me?

Thanks.

Silvia