You need more post. You also have to be a member for a certain amount of time.
Here is the rule 18. The For Sale forum is for contributing members of the site. In order to sell or buy anything in the Marketplace you must have 31+ viable posts, and be a member (including VIP) for at least 45 days to start a sale in this forum. All "For Sale" threads must be posted in the Marketplace only, all other threads will be deleted. Please read the rules that are stickied in that forum.