Can't delete posts or pages

Just wondering if anyone might have any ideas of what's going on with my WPMU install.

When I try to delete a post or page, the browser loads and loads until finally it stops and shows me a blank page. No visible error or anything, just a blank page. When I go back to "Edit posts" the post is still there but the category is now changed to "Uncategorized" (I don't even have "Uncategorized" as an available category in my blog).

Worked fine yesterday, broken today. I've not added, removed, or upgraded any plugins between the time when things were functioning normally and today.

Let me know if you have any suggestions, thanks!