Diagnosis
The backend source system (InfoObject 0BBP_SYS_BE) is emtpy forpurchase order number &1. However, this is an Extended Scenario wherethe purchase order is created in SAP Enterprise Buyer but the goodsreceipt and invoice is in the backend system.
In order to combine the purchase order with the goods receipt andinvoice for reporting purposes, the backend system is necessary.Withoutthis system, data inconsistencies can arise.

Procedure
Check why the Enterprise Buyer System does not specify a backend systemin the purchase order extractor. This may be due to a technical or acoding error. Once you have corrected the error in SAP EnterpriseBuyer,you must save the purchase order again in EBP so that it isupdated properly in SAP BW.
If you have only one backend system, you can enter a fixed value forInfoObject 0BBP_SYS_BE in the transfer rule for InfoSource0BBP_PO_TD_1. Here you use the two-character ID that you defined forthe logical (backend) source system in SAP BW in transaction rsa1 Menu:Tools -> Assignment of Source System for Source System ID.