Updating dunning letter flag using API

Hi,

I had a requirement of updating dunning letter flag for a set of customers for which i had prepared an API to update the flag but while executing i am getting the below error.

DUNNING LETTER:Y

CUSTOMER ACCOUNT ID:392417

CUSTOMER ACCOUNT PROFILE ID:391419

Return Status:E

Error-ORA-06502: PL/SQL: numeric or value error: character to number conversion error

Here is the script

CREATE OR REPLACE PROCEDURE UPDATE_DUNNING_FLAG

(errbuf OUT VARCHAR2,

retcode OUT VARCHAR2)

IS

CURSOR DUNN_FLAG IS

SELECT hca.cust_account_id,

  hca.account_number,

  hp.party_name,

  hp.email_address,

  HPC.DUNNING_LETTERS,

  hpc.CUST_ACCOUNT_PROFILE_ID