I could not reply to the thread already started titled 'Cannot reply'.
I was going to corroborate there that I can't reply to a thread either, getting a message in red -
Unknown error has occured
Tried everything, deleting the quote of the poster I was replying to, then hitting the main reply button at the base of the page instead. Kept getting the error message.
So had to resort to starting a new post on the same subject.
Attaching a screenshot, trying the 'Post Reply' button at the base, get the red Error at the top.