Hi Campaign Monitor,
Your API is problematic (Or the sample code you have provided)
I have filled in the api and list code - thats the only change I've made.
I understand from the forums that you are not hot on PHP, but your example code should work.
In actual fact, the issue has arisen only extremely recently as NuSOAP 0.7.3 was released. For some unknown reason, code which worked perfectly fine under 0.7.2 now no longer works under this newer version. I have gone about creating some new samples (and have one for Subscriber.Add), so if you'd like to get in contact with support, I'll be able to get you the sample that will work under 0.7.3.
My apologies for any inconvenience to anyone else having the same problem, we're looking at getting the new samples up on the site over the next week.
I will download nusoap 0.7.2
Please make a comment in the current sample download
// requires unsoap 0.7.2