Duplicate sales invoice numbers

[Merchant62]

I have multiple user environment and want to obtain uniq sales invoice no for each user
I run update query

ALTER PROCEDURE [dbo].[A_refupdate]
	-- Add the parameters for the stored procedure here
	@gid varchar(5)
AS
UPDATE [SSENTP2].[dbo].[TB_KEY_CONTROL]
    WITH (ROWLOCK) SET COUNTERS =COUNTERS+.000001
   
UPDATE [SSENTP2].[dbo].[TB_KEY_CONTROL]
   WITH (ROWLOCK) SET	voucher=INITIALS+SUBSTRing(STR(COUNTERS,8,7),3,7) 
	 WHERE KEY_ID=@gid

It is not allotting unique invoice number to the users

i will be very thank full if any one guide me to right way

[Rabbit]

We can't help unless we know the table definitions.