[eluser]Needle[/eluser]
Yes, that cjax.php fix appears to have done it! Responses are now coming through as they should.
I can't tell you how pleased I am to finally have this working, I was beginning to think I was crazy! Thanks very much for your help Ajaxboy. CJAX looks like a fantastic framework and I will definitely leave a review once I've had a chance to play with it a bit more.