Problem with Campaign.Create

I'm getting the following erorr when I try to create a campaign through the API:
Campaign.Create Web Service method name is not valid.

I'm using the same method as for all other functionalities in the api, they all work, but I cannot get this one to work. I also had a look at the PHP5-class, but using that is no option (PHP4 user :-( ), but when I compare the code, I'm using the same variables. Are there limitations or am I doing something wrong?

Join 150,000 companies around the world that use Campaign Monitor to run email marketing campaigns that deliver results for their business.

Get started for free