A few hours ago I was performing regular maintenance on one of our sites. I started by updating the all-in-one-seo plug-in. I immediately got an error that the update couldn't be completed because of a server error. Here's what I have done:
1. I deleted and manually uploaded that plug-in. Didn't work.
2. I am using the w3 total cache plug-in and manually deleted the cache. I also edited the .htaccess file and removed the lines w3tc had added. Didn't work. I also edited the wp-config.php file and removed the reference to w3tc near the top. I don't see any other references in that file.
3. I copied the w3tc plug-in back to the server. Didn't help.
4. I delete and recopied TML in an effort to get to the /wp-admin/ login. Didn't work.
Here are the plug-ins installed: Of course, Word Press 3.81, Akismet, all-in-one-seo-pack, Buddy Press and bbpress, bp-group-documents,bp-group-hierarchy, bp-group-organizer, buddypress courseware (not activated), buddypress-docs, buddy-press-media, buddypress-foa, buddypress-registration-groups-1, cimy-user-manager, collabpress (not activated), contact-form-7, events-manager, gd-bbpress-attachments, google-sitemap-generator, nested-shortcodes, shortcodes-ultimate, skysa-official, tag-groups, w3-total-cache, wangguard, wpsso, wysija-newsletters
Additional information: I had just used the BuddyPress plug-in that allows collaboration on documents before all this started. The site has been operating flawlessly for two weeks since it went live.