Might be a timing issue, I do get the occasional error when ?
On one occasion there were several minutes between starting the message and trying to post it.
But once you get it, you can go back, tweak, post 3 secs later and the error repeats.
Every times its occurred, I've been quoting another post.
Don't know if that's a possible cause?
Not a big deal to solve, i cancel the post and redo and it works.
Well, I've tried copying the text of the failed message & starting a new post.
That also got the error.
But when I remove the quoted section, it was accepted......