SAP Message WRF_APC321 - Target purchasing list &1 is already locked by user &2

Diagnosis
The target purchasing list &V1& is already locked by user &V2&.

System Response
The purchasing list cannot be changed. Purchasing list items cannot betransferred or copied to this purchasing list.

Procedure
You can copy or transfer these items at a later time when thispurchasing list is not in use.