PO Matched Invoices are not going for Approval

Hi,

We have enabled AME for payables.

Did AME configurations.

AME is working fine for all Invoices, except PO Matched Invoices.

We are getting the below error when we click on 'View Invoice Approval Histroy':

APP-SQLAP-10000:ORA-06502: PL/SQL: numeric or value error:
NULL index table key value occured in
AP_WORKFLOW_PKG.Get_All_Approvers <-APXIAWHS
with parameters (&PARAMETERS)
while performing the following operation:
set variables from workflow.

If any one has already faced similar kind of issue, please help us.

Thanks

Amar