SRM Invoice Transfer to ERP, Idoc inbound error 51

Hi Guru,

I need a help from you.

the shopping cart, PO, and confirmation are created in SRM correctly, and PO,confirmation are correctly replicated to ERP system.

but the invoice is created in SRM and replicated to ERP system with Idoc status 51 error, showing communication failure, the detail can be seen in attached picture.

what is the reason for this error? how to correct it?

thanks

have a good day

jeff