Why would my /admin/reports/dblog get "stuck" on only showing "page not found" errors? Edit #2: Ok, I finally logged out of my admin account, restarted the browser, then logged back in. Presto! Works. Now that I've thoroughly embarrassed myself, I'll just bow out and go hide underneath a rock.

Edit: Ok, looks like my question wasn't specific enough - sorry! Let's see if I can word this better. Thanks for your patience and to the people who've already taken a swipe at answering this.

I'm having a problem where, no matter what type I select, /admin/reports/dblog refuses to show any results other than for "page not found" entries. As soon as I hit the "Filter" button, it reverts back to the "page not found" results list.

I've tried clearing caches, rebooting Apache, running update.php ... nothing makes a difference. If I try "Clear Log Messages," I get an error screen saying "The website encountered an unexpected error. Please try again later," which is a remarkably unhelpful message. Any thoughts? Thanks!

I haven't added any new modules recently and the dblog results were working fine up until yesterday afternoon. I had made no changes to the site near that time.

I'm not receiving an Error 500 as far as I can tell, as was suggested; it's a generic error message that appears to be one of Drupal's canned messages. If that's not the case, my bad!
Try having a look in your server error_log file that will probably tell you what's causing the problem. My guess is an unsupported character or something has been recorded in a log message.

You could just try clearing the actual log table in the database. Looks like you're on drupal 7 so you'd want to truncate the watchdog table to remove all logged errors