I am not following. The MemberService is for members, and the UserService is for managing users.

You are trying to change the password of a User with the MemberService?

I'm sorry, I stated it incorrectly.

I am using the UserService. Here is my code, with some parts removed for security:

            IUserService uSvc = appContext.Services.UserService;
            var allTypes = uSvc.GetAllUserTypes();
            IUserType adminType = allTypes.Where(t => t.Alias == "admin").FirstOrDefault();
            string[] allSections = { "content", "developer", "media", "member", "settings", "users" };

            aUser = uSvc.CreateUserWithIdentity("myUserId", "[email protected]", adminType);
            aUser.Name = "My user";
            uSvc.SavePassword(aUser, "some password");
            aUser.Language = "en-US";
            foreach (string aSection in allSections)
            {
                aUser.AddAllowedSection(aSection);
            }
            uSvc.Save(aUser);

Hey, I am having a similar issue with a newly installed Version of Umbraco version 7.6.3 assembly: 1.0.6361.21154. Although mine is with members.

//convert model to Member
        var newUser = Services.MemberService.CreateMember(model.Email, model.Email, model.Email, "User");
        newUser.SetValue("inGameName", model.Username);

        memberService.Save(newUser);
        memberService.SavePassword(newUser, model.Password);

I've tried saving the password before save the member or after and couldn't find any information about whats wrong

is working on a reply...