Pretending to be an Paypal API Problem

… and now the Paypal Portlet tells me:
“You do not have permissions to make this API call”

What is the reason?

I have an API signature, username and password and now i checked them a few more than twice.

Why should Paypal give me the neccesary data without giving me the permission?

And where is the problem in fact?

Here is the germanduplicate Entry … and it seems to be solved.