AdWords API Please help me, Always response - The client does not have permission to perform the requested operation. :(

Hello All,

I have tried the methods like get all campaigns, adgroups, keywords;
add new keyword... but I always received the error code 4: The client
does not have permission to perform the requested operation.

But when I tried to schedule & get report, it works perfectly.

Please can anybody help me with this problem?

Thank you a lot!
Sergio