Dynamics CRM 2011 Plugin - an unsecured or incorrectly secured fault was received from the other party

Hi,

I am getting the following error with one of my plugins:

"An unsecured or incorrectly secured fault was received from the other party"

My CRM 2011 is on premises, and the error is sporadic.

This error is being thrown by I method executing a RetrieveMultiple (QueryExpression):

This is how i create my IOrganizationService:

    var organizationUri = new Uri(orgUrl);
                var credentials = new ClientCredentials();
                var deviceCredentials = Microsoft.Crm.Services.Utility.DeviceIdManager.LoadOrRegisterDevice();

                credentials.UserName.UserName = username;
                credentials.UserName.Password = password;

                var serviceProxy = new OrganizationServiceProxy(organizationUri, null, credentials, deviceCredentials);

                serviceProxy.ServiceConfiguration.CurrentServiceEndpoint.Behaviors.Add(new ProxyTypesBehavior(Assembly.GetExecutingAssembly()));
        
                service = serviceProxy;

Any ideas?

Thanks