The same error's come up knocking chat out as yesterday:

:(

Object reference not set to an instance of an object.

Shows up as a dialog box when trying to send a message when you're already connected, or when trying to send a message or load a chat.

Yesterday this knocked chat offline. Happened just now sometime just after 3:30 AM UTC+0.

For those unaware this happened as well yesterday for the first time.

Also for the time being there is the Testing server main channel. Anyone who's joined the site since early February might not have their account ported over to the Testing server yet, and might not be able to log in - you'll have to re-register. Bonus points is, if the site goes down there too, apparently it'll be relatively easier to diagnose what happened!

up again for now

seems to be stabilized for now. It may come back, it's a bit rather hard to reproduce. However, the site is setup such that I will be able to determine more information about it the next time it occurs

Chat's gone down again like Xija says. The error's different this time:

:( Sequence contains no matching element

Given the new error - "Sequence contains no matching element" - I'm going to get off my butt and post another bug I noticed recently. It may be related to what's happening now, because it relates to characters being added/removed from the user list in a buggy manner: joining the same channel from another tab can silently make the first one fail (litphoria.com)

Deployed a fix. This should no longer appear.