The Captcha relies on both the GD library and the Free Type Library, is free type also enabled?
Send a link to the registration page so i can see the problem to investigate.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.