When I'm looking at the unanswered posts, I'm often unable to go to the next pages. Clicking on "Next" or "Page x" doesn't matter.
It will usually say something like "No Topics Meet Your Criteria". I have found that if I delete the sid in the url then click on "Next" it will work.
I see this in FireFox. I haven't tested it in IE or Opera.
Hopefully someone else has noticed this and can back me up...