error while using Cast function in oracle

Thnx....that worked and the sp has compiled now.
But still it does not execute.

I am getting the below error while executing:
The following error has occurred:

ORA-06502: PL/SQL: numeric or value error: character string buffer too small
ORA-06512: at "STRL.SP_BEDOCC", line 22
ORA-06512: at line 9

My sp till line 22 is as follows:
CREATE OR REPLACE PROCEDURE sp_bedocc
--exec sp_MISMonthlyBedPosting '15 may 2002','23 july 2002'
--sp_helptext sp_bedocc
--drop proc sp_bedocc

(
v_fin_year IN NUMBER DEFAULT NULL ,
v_month IN CHAR DEFAULT NULL
)
AS
--Exec sp_los @fin_year , @month
v_fn_yr Number(10,0);
v_yearmonth CHAR(6);
v_yr NUMBER(10,0);
v_temp NUMBER(1, 0) := 0;


BEGIN

v_yr := v_fin_year ;
v_fn_yr := v_fin_year ;
v_yearmonth := TO_CHAR(v_fin_year,'9999') || v_month ;