Creating users through core_user_create_user

Hello all,

I'm newbie to Moodle and it's web services usage. I need to call the core_user_create_user function from C# in order to replicate the creation of users in some other solution. This achievement will be done by calling the web service on the fly when the user is actually created in the fist solution.

I've done all the set up needed for this purpose (Gone throrgh the following tutorial: https://docs.moodle.org/28/en/Using_web_services) and used some example I found on the web to test if it work without success. I keep receiving the following message: 

{"exception":"webservice_access_exception","errorcode":"accessexception","message":"Excepci\u00f3n al control de acceso"}

If I try to call some other function I end up receiving the same response.

Attached you will find the code which I'm using.

Any comments or suggestions will be really appreciated!

Thanks a lot in advance!