Once again I am baffled

I have a table (invoice_head) with a Primary numeric key index (invroice_numb)
And a table with incrementing numbers (remote_sys)

The tables are not buffered

I say
SELECT remote_sys
IF RLOCK()
ln_invoice_numb = remote_sys.invoice_numb
REPLACE remote_sys.invoice_numb WITH remote_sys.invoice_numb+1
UNLOCK
ENDIF
INSERT INTO invoice_head (invoice_numb, location_id, customer_id, issue_date, ;
shipping, login_id, req_numb) VALUES (ln_invoice_numb,ln_location_id, ;
ln_customer_id, DATE(), ' ', 'SMcLaughlin', 0)
INSERT INTO invoice_lin (invoice_numb) VALUE (ln_invoice_numb)
SELECT invoice_head
SET ORDER TO TAG invoice_numb ********
SEEK ln_invoice_numb
pn_recno = RECNO()

yet after multiple users run this code I get a index tag not found (********)
and if I browse the table ordered by invoice_numb they are out of order and not even a reindex straightens them out???

Has anybody else had problems with insert into on a primary field?

Thanks in advance for any and all help or insight

Stephen McLaughlin
krsone@charm.net