SAP Message WRF_PRC_POHF221 - Synchronization of allocation table is not possible (quantity change)

Diagnosis
The system was unable to perform the synchronization of the allocationtable &1 item &2. As a result, it was unable to change the purchaseorder quantity.

System Response
The system was unable to perform the quantity change because theallocation table synchronization failed.
Follow-on documents probably exist for the allocation table that arepreventing the change to the purchase order quantity.