Yes, there are requirements. Curl is the major one. But the ability for the server to resolve DNS is also important. There is a test script here to see if things pass. http://www.boonex.com/forums/topic/Test-script-for-curl-fopen-and-gethostbyname.htm
You must also have the facebook side setup properly as well. The two biggest problems are the domain and site url settings. www is technically a sub domain, so if the dolphin site is not using it then it cannot be setup that way in facebook. The url must match perfectly. Additional settings.http://www.deanbassett.com/images/facebook_screenshots/
Deano I have run your dbtest.php and all has passed. I have looked at the facebook screen shots and wanted to let you know that FB has changed the GUI for their app settings could you update your screen shot tp match the new settings page for facebook. It might help new people installing the app.