Just experienced a problem wherein I wrote a post that refused to display! In the Manage->Pages page, if I clicked on the post's category link I get a blank page.
Turned out the problem was that I had changed a Category name and hadn't also changed the slug-tag and that was fouling things up. I DIDN'T change the category name back; I just changed the slug to read the same (with "-" 'tween words) and all is well again. When in doubt, re-boot then think back to the last 2-3 things you changed and retrace your steps. If that doesn't work, Wild Turkey.