If you have a large inventory (I'm guessing 15k items +) it will take an inordinate amount of time for the pages to load. It takes it a full minute for me and sometimes it times out, but after a refresh and a bit more waiting it usually comes up. Your issue could be entirely separate from the issue I've had, but I thought I'd throw it out there in case you guys weren't waiting quite long enough.
I'm pretty sure it's got something to do with the inventory calculator since this sort of stuff didn't happen until after they put that up. Since the calculator reconfigures inventory worth every hour, this issue also happens every hour.