A week ago, I was trying to post several link urls. My first list had five urls -- when I tried to do a preview, I got an error message of some kind. I sensed that it might be caused by the url list. So I deleted first one and then a second one. When there were only three links in the message, the preview appeared instead of an error message.
Another thing I've noticed with this and some other forums is that if you are taking a long time to write your message and do not do a preview every now and then the program things that you have walked away and will "time you out."
Brian Norden