How To Return Unique Identifier In SP

I have trouble to get the uniqueidentifier I just inserted out.

---sp
CREATE PROCEDURE dbo.FAC_Ins_USR
@LAST_NAME AS nvarchar(60)
,@FIRST_NAME AS nvarchar(60)
,@NewID uniqueidentifier output
AS
BEGIN

[Code] ....

The new data went into the table, and the print @myErr shows 0.

But print @myID shows nothing.

---here is the part of the table

CREATE TABLE [dbo].[USERS](
[USER_ID] [uniqueidentifier] DEFAULT NEWID() NOT NULL,...