There is likely a limit of one post per minute per user built into the software. This is probably (although, admittedly, a guess) a way to stop robots from flooding the site with thousands of posts per minute.
In addition, I’m going to guess that someone is a Simon & Garfunkel fan.
I got thst message yesterday whwn I clicked twice because the first time I thought didn’t go throgh. too fast for the system I guess. A lesson in patience!