Quote:
I set a password for each level in the publication
If by 'level' you mean 'Chapter', then it just might be the way Opus works. If you had...
Chap1 as Intro (no pw)
Chap2 subject blah-blah (pw xyz1)
Chap3 subject other blah-blah (pw xyz2)
etc...
If your student is going to start in Chap1, then Chap2, then Chap_n for example.... he/she will be prompted for each chapter's pw upon opening any page in that chapter.
However, if Chap1 were essentially a menu page or a table of contents page, and from there the student went directly to a page in Chap2 he would only be prompted for chap2 pw.
If that does not answer enough, do as Steven says and post your .imp file as an attachment here.
Cheers and Welcome to the forum.