 <p>You have to enable early bound entities by calling</p> <pre><code>_serviceProxy.EnableProxyTypes(); </code></pre> <p>on your OrganizationServiceProxy instance.</p> <pre><code>var cred = new ClientCredentials(); cred.UserName.UserName = "your username"; cred.UserName.Password = "your password"; using (var _serviceProxy = new OrganizationServiceProxy(new Uri("https://[your organization service url here]"), null, cred, null)) { _serviceProxy.EnableProxyTypes(); // Will throw error on save changes if not here var context = new CrmServiceContext(_serviceProxy); context.AddObject(new Opportunity() { Name = "My opportunity" }); context.SaveChanges(); } </code></pre>