I've succesfuly implemented Facebook login on Umbraco in my local development environment running Umbraco 6.0.5.

On the production server however, i only get errors when trying to login with Facebook.

I have located the problem to the method Member.AddMemberToCache. If i comment out those two rows i don't get any errors (but the member isn't logged in either).

MESSAGE: Exception has been thrown by the target of an invocation. STACKTRACE: at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
 at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
 at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
 at Umbraco.Web.BaseRest.RestExtensionMethodInfo.Invoke(String[] parameters) INNEREXCEPTION: System.NullReferenceException: Object reference not set to an instance of an object.
 at MyProject.FacebookLogin.createNewUser(Object facebookUser)
 at MyProject.FacebookLogin.LogUserIn()

Here is a piece of my code that is throwing errors.

private static String createNewUser(dynamic facebookUser)
        {
            MemberType siteUser = new MemberType(1088); // Facebook user type
            Member newMember = Member.MakeNew(facebookUser.name, facebookUser.id.ToString(), facebookUser.email.ToString(), siteUser, new umbraco.BusinessLogic.User(0));

            Member.AddMemberToCache(newMember);
            return newMember.Id.ToString();
        }

Umbraco version is 6.1.1. I didn't have this problem in 6.0.5.