Oracle 9i compile error PLS-00382: expression is of wrong type

The following procedure worked fine all along.  When Oracle 9i was installed,
I suddently get compile error:  PLS-00382: expression is of wrong type
See line with arrow.   What's the solution to this problem?
Please help.
Thanks.
Alad
PLS-00382: expression is of wrong type
FUNCTION f_cov_count(covcode IN VARCHAR2,SEGMENT IN VARCHAR2)RETURN cursorType
IS
ref_cur cursorType;
res BOOLEAN:=FALSE;
ncount NUMBER;
BEGIN

    IF ref_cur%isopen THEN
         CLOSE ref_cur;
    END IF;

    SELECT COUNT(*) INTO ncount FROM simdata.L_SEGMENT
    WHERE coverage_code = covcode AND segment_number=SEGMENT;

    IF ncount > 0 THEN
        res:=TRUE;
    ELSE
        res:=FALSE;
    END IF;

    OPEN ref_cur FOR SELECT res AS res FROM dual;   //<-- I get error here.  What's the solution to this problem?

    RETURN ref_cur;
END;