It's called "ghosting" and it's craig'slist's dirty little secret; it's how they combat what they think is spam. They trick you into thinking your ad is posted, you can see it, but it is nowhere to be found on the site. http://craigslistpostingsecrets.wordpress.com/2008/03/08/ghosting-on-craigslist/ You might have posted too many ads and got flagged for abusing the system somehow. The only way for you to post again would be to use a different email address, your old account will never work again. It has been flagged, and everything you try to post will be ghosted from now on.