Use the Items Locked report to identify which purchasing documents are locking the item.
Navigate to Standard Reports > Troubleshooting > Items Locked.
Use the right-click menu in the report to Apply Column.
Filter by the locked SKU to quickly identify the related purchasing documents.
Resolve the lock by completing one of the following actions for each affected PO:
Cancel the PO.
Update the ordered quantity for the item to 0.
Convert the PO to a receipt or invoice.

After resolving all purchase orders that lock the item:
Return to the item record.
Confirm that the vendor field is editable.
Click Refresh Data if the item editor does not update immediately.