Hi Silvia, that happened to me a lot in the early days of my membership here. I pm’d Travis Smith to ask him to check if there was a problem. He said “...some messages get held, and others get posted, and it?s the blog software that determines if it?s ?odd-looking? enough to be held. I don?t know exactly how the interpretation works.”
It sorted itself out in time. Meanwhile it was a big mystery and a bit upsetting. If you’d like Travis to check out what’s happening in your case, contact him. Click on his name in his latest post in the Forum Announcements section and send him a private msg.