INVALID_PARTY_CONTEXT issue in IBY_DISBURSEMENT_SETUP_PUB.SET_PAYEE_INSTR_ASSIGNMENT

I am doing a Supplier Bank and Bank Account conversion from R11 to R12. This is for external bank account.

Got INVALID_PARTY_CONTEXT result code when using the IBY_DISBURSEMENT_SETUP_PUB.SET_PAYEE_INSTR_ASSIGNMENT.

I can't find any solution for the same issue here.  Please help.

Below is the anonymous block:

DECLARE

    xAssignID                     NUMBER;

    xReturnStatus                 VARCHAR2 ( 2000 );

    xMsgCount                     NUMBER ( 5 );

    xMsgData                      VARCHAR2 ( 2000 );

    pPayee                        IBY_DISBURSEMENT_SETUP_PUB.PAYEECONTEXT_REC_TYPE;

    pAssignmentAttribs            IBY_FNDCPT_SETUP_PUB.PMTINSTRASSIGNMENT_REC_TYPE;

    xResponse                     IBY_FNDCPT_COMMON_PUB.RESULT_REC_TYPE;

    pInstrument                   IBY_FNDCPT_SETUP_PUB.PMTINSTRUMENT_REC_TYPE;

    vInstrumentID                 NUMBER;

    vBankName                     VARCHAR2 ( 100 );

    vVendorName                   VARCHAR2 ( 100 );