Sorry - I was just double checking the settings in the admin area. As mentioned there is system that only allows you to post ads if you've been a member for longer than 7 days and posted at least 15 messages. This was introduced because we had a few people register on the site obviously with the sole purpose of just advertising stuff for sale and not too concerned about contributing.
As you've been a member for a few years now I've just promoted you to the relevant group so hopefully you should be able to post your advert. The only real stipulation we have is for you to name an asking price for what you'd like to get - i.e. nothing vague asking for offers.
Go to your first post in that thread. Top right hand corner is a "Thread Tools" caption which allows access to a drop down menu which inludes an option to "Edit Title"
Dave