Engage Interaction doesn't load after publishing course

Hi to all.

I prepared a course containing different engage interactions. The strange thing that's happening is, that after publishing one or more interaction do not load at all. I can page forward and backward but nothing happens, the page is empty. I tried to delete from presenter all engage interactions, and adding them afterwards bit with no success.

Even if I change the order... the first interaction doesn't appear. The interactions put at the end of the course do appear.

Have somebody any ideas?

Thanks a lot.