OrganizationServiceProxy Error Need help please

I want to send email using Microsoft Dynamics Crm 2011 plugin. but when i try to create Organizationserviceproxy it gives me error, the error is Shown below

Exception : Fehler bei der Anforderung des Berechtigungstyps "System.Security.Permissions.SecurityPermission, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089".    bei Microsoft.Xrm.Sdk.Client.ServiceConfiguration`1..ctor(Uri serviceUri, Boolean checkForSecondary)    bei Microsoft.Xrm.Sdk.Client.OrganizationServiceConfiguration..ctor(Uri serviceUri, Boolean enableProxyTypes, Assembly assembly)    bei Microsoft.Xrm.Sdk.Client.ServiceConfigurationFactory.CreateConfiguration[TService](Uri serviceUri, Boolean enableProxyTypes, Assembly assembly)    bei Microsoft.Xrm.Sdk.Client.ServiceProxy`1..ctor(Uri uri, Uri homeRealmUri, ClientCredentials clientCredentials, ClientCredentials deviceCredentials)    bei only_Email.Plugins.EmailSend.Execute(IServiceProvider serviceProvider)

And down below is my code

Uri homeRealmUri = null;

ClientCredentials credentials;

Uri organizationUri;

credentials = newClientCredentials();

credentials.Windows.ClientCredential = newNetworkCredential("xx","xx","xx");

string orgUrl = http://xx/XRMServices/2011/Organization.svc;

organizationUri = newUri(orgUrl);

using (OrganizationServiceProxy _serviceProxy = newOrganizationServiceProxy(organizationUri,

                                                                                    homeRealmUri,

                                                                                    credentials, null))

{

}

Please if anyone can help. and yeah i m using on premise dynamics crm 2011