WS call Dynamics V9 online permissions plugin

Unhandled Exception:
The type of the first permission that failed was:
System.Security.Permissions.SecurityPermission
The demand was for:<IPermission class="System.Security.Permissions.SecurityPermission, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=xx"
version="1"
Flags="Assertion"/>

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "GET";
            response = request.GetResponse();