pl/sql PROBLEM WITH VARIABLES IN EXECUTE IMMEDIATE

Hi,

I have got litte problem with pl/sql and function:execute immediate .

Example, it is a script:

my variable:='2007-01-07'; <----- my variable

--
SQL_:= 'create table imago_test  SELECT PART_NO,
         SUM(DECODE(DIRECTION,''+'',QUANTITY,''-'',-QUANTITY,0)) AS
ILOSC,
        ROUND(SUM(DECODE(DIRECTION,''+'',QUANTITY*COST,''-'',-
QUANTITY*COST,0)),4) AS WARTOSC
  FROM ifsapp.INVENTORY_TRANSACTION_HIST2
  WHERE     LOCATION_NO in (''MG'',''MW'',''MG1'')
          AND    PART_NO LIKE ''071-001-001%''
          AND DATE_APPLIED<=NVL(TO_DATE('''||my variable||''',''YYYY-
MM-DD''),SYSDATE)
  GROUP BY PART_NO';

execute immediate SQL_;


and it gives me  error message: error number or value

pls let me now asap

thx