Problem with Ora-06512 at string line string

What is this Error means? i have create all the function and procedures but i counlt work. It show this error messge when i executes a procedures.
i have my procedures like this..
CREATE OR REPLACE procedure getPostcode (v_postcode IN OUT NUMBER,
v_suburb IN VARCHAR2)


IS
BEGIN

SELECT dbp_postcodes.postcode
INTO v_postcode
FROM dbp_postcodes INNER JOIN Helens_data
ON dbp_postcodes.Locality = Helens_data.Suburb
WHERE dbp_postcodes.State = 'NSW'
AND suburb = v_suburb;


END getpostcode;
Then, i called out
/* Start finding the postcode and insert*/

IF (check_suburb(r1.suburb) = TRUE) THEN
IF ( v_valid = TRUE ) THEN

error show this line --> getpostcode(v_postcode, r1.suburb, null);
insert_data(r1.id, r1.fname, r1.surname, r1.company, v_stnumber, v_stname, r1.suburb, v_postcode, v_comments);

I doing a assignment on the address databse. So, table of Helens_data
dont have a postcode, so i need to find from the helensdata.suburb with the dbp_postcodes.locality.
to find the relevant postcode.
Why this Error show to me?

You have a syntax error - you are calling the procedure with 3 arguments - you declare it as taking 2 arguments.

thanks.