Need assist w/ BEFORE INSERT trigger

Oracle 8.1.7

We have several apps, each with its own db, that insert rows into a table on a central db. Call this table MSG_ROUTER. These rows are picked up by a process that translates them to e-mails. Each row has to have a unique id. So a sequence was defined in the DB hosting MSG_ROUTER, and the apps get the next key value from that sequence.

I was just made aware of this when a developer came to me and couldn't get her insert statement to work. After hearing that several apps, from several db's were inserting into this one table and jumping hoops to keep a sequence generated PK, I proposed we simply create a before insert trigger so the db could take care of the PK and get the apps out of that business. So of course it fell to me to write the trigger, which I've only done once before, and that over a year ago, after which that project was tossed out.

Here's what I have:

CREATE OR REPLACE TRIGGER TRG_MSGRTR_FORCE_PK BEFORE INSERT
ON MESSAGE_ROUTER
REFERENCING OLD AS OLD NEW AS NEW
FOR EACH ROW
begin
:NEW.MSGRTE_MSG_SEQNBR := SQ_MSG_SLNO.NEXTVAL; END;
/

which yeilds this error

PLS-00357: Table, view or sequence reference 'SQ_MSG_SLNO.NEXTVAL' not allowed in this context. Received on Fri May 14 2004 - 12:43:42 CDT