I tried to upgrade Post-Plugin Library from 18.104.22.168 to 22.214.171.124 from the plugin management screen. The upgrade was successful, but the plugin wasn't reactivated.
Now I can't access the admin interface: I get blank pages. My blog works fine, though.
I tried to remove the files from the server and uploaded the 126.96.36.199 manually. Didn't work. I tried replacing the files with 188.8.131.52, which definitely worked. That didn't help either.