captcha solving 'API integration' CURL/PHP

Using a captcha solving service 'deathbycaptcha' I can't get it working with a form submit that requires a captcha. Currenty I've written a PHP curl script to download the form, save PHP session ID, then solve the cache, then submit the data again to the same page, but it keeps returning invalid captcha even though the service has correctly solved it. Shouldn't be to dfficult for an experience programer, after all this service exists so there must be a way to do it? I just can't find it. PM me with details on how you plan to do it. If you know what your doing it shouldn't take too long, I imagine it's only a few lines of code. Thanks