Item &1 is being processed (user &2)

What causes this issue?

You want to delete a changeable version item in sales document &V1&.
The system has to prepare to transfer the changeability to the original
document. However, the document is currently being processed by user
&V2&.

System Response

The item cannot be deleted while the document is locked.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.