Selecting Unique Record

I have a stored procedure (below), that is suppose
to get a Reg Number from a table, (Reg_Number), in
such a way that every time the stored procedure is called,
it will get a different reg number, even if the stored
procedure is called simultaneously from two different
places,

However it is not working that way.

If two different users access a function in there
VB program at the same time, the two different users
will get the same reg number.

I have looked at the stored procedure, it looks foolproof,
yet it is not working that way.

Thanks in Advance,

Laurence Nuttall
Programmer Analyst III
UCLA - Division of Continuing Education

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Here it is:

CREATE PROCEDURE sp_GetNextRegNum
@newRegNum char(6) = NULL OUTPUT
AS
LABEL_GET_ANOTHER_REG:

Select @newRegNum =(select min(Reg) from reg_number)

IF Exists (select Reg from reg_number where reg = @newRegNum )

Begin
Delete from reg_number where reg = @newRegNum

IF @@Error <> 0
Begin
Goto LABEL_GET_ANOTHER_REG
End
--Endif
End

ELSE
GoTo LABEL_GET_ANOTHER_REG
--Endif
GO