Why Wont Craigslist Let Me Post An Ad?

1. You may not post "essentially the same item" before deleting the old item. This applies even when posting in a different city or category. So if your post lends itself to more than one category, you need to alternate the categories. 
   
   Workaround: You may be able to overcome this restriction by setting up an additional account with a different email address.
   
   
2. Your post may not contain a link "to a commercial website or auction." This is an example of a rule I haven't been able to find anywhere, until I was blocked for violating it! You may have to guess whether Craigslist will consider the linked site "commercial." Craigslist's current enforcement of this restriction seems to be minimal.
   
   You'll be entirely safe if you don't link to any website, but instead invite the reader to email you for more information (very easily done--see below). This option however involves the risk that your reply may be blocked by a spam filter (even though your message isn't spam). You may always give a Web address as non-linking text, or link to a webpage without any links on it.
   
   
3. You may not exceed your "volume limit." As I write this, Craigslist doesn't define the volume limit in any way, but will reject a post for this reason. Try the workaround for restriction 1, above. Or just re-try ten minutes later.
   
   
4. The Posting Description cannot be longer than 1000 characters. The Posting Description is your entire post exclusive of the title. This seems to apply only to paid listings, so otherwise it's probably safe to ignore it.

These are taken from my article about Craigslist, which may give you other useful information.