Short version: List view buttons [>] [>>|] [Update] don't work.

Long version: I can't use the next page button in the list view (of any module), nor the end of list or the update button. I get the following error page:
Forbidden
You do not have permission to access this document.
I'm sure it's some sort of permissions issue, but as far as I know (and can see) every file has all the rights it can have.

I can sort the items in the list view just fine.

Running: SugarCRM 5.1.0b (updating to 5.2 is going to be problematic at the moment) on a shared linux server.