I was answering a question, and suddenly I got the following error twice in a row.
Why is this error occuring? Can I do anything to avoid it?
This is actually related to your other question. What's happening is a security violation. Something must be seriously broken with your browser or with a proxy you're behind. Looking at the logs, it seems it's deciding at random whether it should send your user cookie or not.
Some internal error must have occurred. Possibly a deployment just a you were posting yoru answer (as @Sha Dow Wiz Ard suggests in his comment).
On a vary high transactional site like StackOverflow this will happen on occasion - there is nothing you personally can do about it.
The exact reason this might occur is knowledge that only Stack Exchange employees will have (and maybe a few other privileged people) - but, no, as per the message on the page, this is an error on their side and nothing you can do about it.
Someone might thank you for bringing this to attention if they're unaware of it being a persistent, recurring issue, but I'm sure SE will know of it and either A) fix whatever caused/is causing it, or B) leave it, as it occurred under exceptional circumstances at a specific time which is out of their hands.
I faced this error when I lost the session Connection from
StackOverFlow site and refresh the my page. This happened because my internet connection was changed from one gateway to another gateway. It doesn't happen normally with regular StackOverFlow site page, but yes, it always happens in Chat Room's Access Page.