Error when posting

Someone tried to post an introduction for the OpenVillage Festival and he got this error. Anyone know what went wrong / how to fix it?

Well … I had the same error this morning. Turned out the whole site was down for around 6 hours, until I could fix it at ca. 9:50. Everything back to normal now.

(Our Redis caching server had crashed, and was not included in our automatic monitoring yet. We’ll include it now, to prevent any recurrence of that type of error.)

Thank you! Meanwhile he also got it working and successfully posted.