Expression is of wrong type

This is a function to check whether the given date is a holiday or not. Holiday_master table contains a list of all holidays. The function is complied well. This is the code of function:

CREATE OR REPLACE FUNCTION IS_HOLIDAY( CHECK_DATE IN DATE )
  RETURN BOOLEAN
IS
  RETURN_VAL BOOLEAN;
  CNT  NUMBER(3);
BEGIN
RETURN_VAL := FALSE;
 BEGIN
 SELECT COUNT(*) INTO CNT FROM HOLIDAY_MASTER
 WHERE FROM_DATE <= CHECK_DATE AND TO_DATE >= CHECK_DATE AND
RECORD_STATUS='ACTIVE';  RETURN_VAL := TRUE;  EXCEPTION  WHEN
NO_DATA_FOUND  THEN RETURN_VAL := FALSE;  END;

  RETURN RETURN_VAL;

EXCEPTION
WHEN NO_DATA_FOUND THEN
RAISE_APPLICATION_ERROR(-20005,'Error (NO DATA FOUND) while Calculating
Dates for Esclation or To Be Rectification Date for Date : ' ||
CHECK_DATE); WHEN OTHERS THEN RAISE_APPLICATION_ERROR(-20006,'Error
while Calculating Dates for Esclation or To Be Rectification Date for
Date : ' || CHECK_DATE);

-- Data_Replication_Error_Log(SQLCODE, SQLERRM, NULL,
--  'Date Error: ');
END;
/

When I execute this using the following statement:

select is_holiday('25-DEC-2006') from dual

I am getting an error like this: "ORA-06552: Statement ignored ORA-06553:PLS-382: Expression is of Wrong Type." What is the problem here? Why am I getting the error? Thank you.