ASPNETDB.MDF-uniqueidentifier

Hi:
I am using the built in securty database from vs2005
I am trying to write an insert trigger that will add a role each time a user is added but I seem to be having difficulty I believe it's with the uniqueidentifier datatype. when I run this trigger via an insert statement I get the following error.
Can anyone set me straight?
========error==============
Cannot insert the value NULL into column 'RoleId', table 'R:AAAPROJECTSASPVS2005MERCERBUCKSAPP_DATAASPNETDB.MDF.dbo.aspnet_UsersInRoles'; column does not allow nulls. INSERT fails.
==================insert statement==========

Declare @NewUserID as uniqueIdentifier
set @NewUserID=newID()
print Cast(@NewUserID as varchar(50))
insert into dbo.aspnet_Users (ApplicationID,UserID,UserName,LoweredUserName,LastActivityDate)
Values('f23f01f0-7ad7-463b-87e2-f3e9141e6426',@NewUserID,'lrchase','lrchase','7/20/2005')
======trigger============================
set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go


ALTER TRIGGER [InsertRole]
ON [dbo].[aspnet_Users]
AFTER INSERT
AS
DECLARE @RoleID uniqueidentifier
DECLARE @UserID uniqueidentifier
Select @UserID=Userid from inserted
Print @UserID
SELECT @RoleID = RoleID
FROM dbo.aspnet_Roles where dbo.aspnet_Roles.LoweredRoleName='user'
Print @RoleID
SET NOCOUNT ON;
Insert Into dbo.aspnet_UsersInRoles
Values(@UserID,@RoleID)

Thanks Len