Changing Supplier on PO not replicated from SRM to ECC

Hi,

We have requirement where buyer should be able to change vendor on PO in SRM and the change should be replicated to ECC.

Currently in our SRM system once shopping cart is fully approved, follow-on-document (Purchase Order) is created in SRM and is replicated to ECC (Extended Classic Scenario). Later when buyer change Supplier on the PO in SRM the change is not replicated to ECC.

When I put break point in FM 'B46B_DPO_TRANSFER' at 'CALL FUNCTION 'BBP_PO_INBOUND' DESTINATION lv_destination' the ' lt_bapi_return' table is filled with two entries, one of the message is 'Change Vendor could not be effected'.

Is there any missing configuration or any BADI that needs to be implemented to fix this. We are on SRM 7.03.

Thanks in advance

Abhiram.