我不确定为什么会收到此错误消息。我在我的sql数据库中为其定义了一个主键。这是我的代码:[HttpPost]publicActionResultRegister(RegisterModelmodel){if(ModelState.IsValid){//AttempttoregistertheuserMembershipCreateStatuscreateStatus=MembershipService.CreateUser(model.UserName,model.Password,model.Email);if(createStatus==MembershipCreateStatus