The "sess_longsequenceofhexadecimal" is your PHP session ID. Don't post it; it could potentially be used to access your account.

This generally means a server administrator done screwed up: "No space left on device" means the server's hard drive is full. Most likely a log file grew too big, but there's tons of things that could cause it. User content is probably stored on a different server, which is why posting still works.

So basically it's not your fault and you can't do anything about.

It's perfectly possible as long as you don't live on Earth (and don't mind a scifi/fantasy aspect).