Set_Payee_Instr_Assignment - Status E - No Error Message

I'm attempting to use IBY_DISBURSEMENT_SETUP_PUB.Set_Payee_Instr_Assignment to assign an existing bank account to an second supplier/site.  I have already SUCCESSFULLY set up the second supplier as a joint owner of the account.  There are virtually no messages from the API - all I get is Status E, ORA-00000 (SQLERRM) and "IBY" (Msg data) <---- seems like the beginning of a message, but there is no other output.  Any suggestions on how to determine what the actual error is??  My code is listed below...  I've also verified that the query returns proper values for the supplier site id and party site id.