why 1002-fetch out of sequence?

From: Andrew P.Sandimirov <A.Sandimirov_at_vaz.ru>
Date: Thu, 11 Feb 1999 09:53:17 +0400
Message-ID: <79tnin$cgn$1@ss20.vaz.ru>

Hello All.
Why in IF block commit make error:
ORA-01002: fetch out of sequence

DECLARE

        err number;
        CURSOR NS1 IS SELECT PRIM FROM NS where ndet like '21%' FOR UPDATE
OF PRIM;
        NS_RECORD NS1%ROWTYPE;

BEGIN
OPEN NS1;
LOOP
FETCH NS1 INTO NS_RECORD;
EXIT WHEN NS1%NOTFOUND;

        update NS set PRIM = PRIM WHERE CURRENT OF NS1;
        IF MOD(ns1%rowcount,100) = 0 THEN
                COMMIT WORK;    /* it is HERE*/
        END IF;
        END LOOP;

CLOSE NS1;
EXCEPTION
WHEN OTHERS THEN
ERR:=SQLCODE;
INSERT INTO A(POLE) VALUES (ERR);
END;
/ Received on Wed Feb 10 1999 - 23:53:17 CST