I'm getting this when trying to post stories to my army fluff thread.
I thought it was linked to the length of the posts.
It then looked like it was based on the content of the post. I've been narrowing it down to some kind of corrupting character or something.
It also seems to block my IP temporarily after I've hit the 403 too many times. Currently getting a Connection Timed Out error when accessing on my home network. I am posting this using my mobile internet.
As soon as it comes back I'll check the possibility of a corrupt character as I'm down to a word which is giving me a 403.
I'll check the delivery payload for anything odd