Apparently (via registrar), there are classes that beanweb knows about, that can be signed up for, but shouldn't be viewable by the students. However, they can still put in the CRN and sign up for it until, suddenly, they aren't assigned a classroom or teacher. They then come into the registrar's and they sometimes have to rebuild them an entire schedule.
I don't have any way to test this, but I know part of it is because they're doing it in the production environment (which is a problem we have no control over). Until they get that fixed, it might be that we have to be able to pull which years/semesters/classes are currently available for viewing or dive into the HTML to see if there's a 'unavailable' option (e.g. disabled or hidden).