Regarding PrincipalUpdate

I am trying to add a user through PrincipalUpdate method however I am getting error "no-access" and code is "denied" however I am Adimistrator-Limited and can create user through UI can't I create user through coding I am using .net and AdobeConnectSDK for the same below is my code.

objectPrincipalSetup =

new AdobeConnectSDK.PrincipalSetup();

objectPrincipalSetup.email = stringUserEmailAddress;

objectPrincipalSetup.login = stringUserEmailAddress;

objectPrincipalSetup.password = stringUserEmailAddress;

objectStatusInfo = objectAdobeConnectXmlAPI.PrincipalUpdate(objectPrincipalSetup);

am I missing something. Also what is the difference between service URL https://connectproxxxxxxx.acrobat.com and "https://connectproxxxxxxx.na5.acrobat.com"

Can anyone help!