The handling unit &1 is assigned to delivery &2 and cannot be processed

What causes this issue?

Handling unit &V1& is assigned to delivery &V2&.

System Response

The stock posting from the usage decision cannot be made for this
handling unit.

How to fix this error?

Check whether you can delete the assignment of handling unit
&V1& to delivery &V2& or whether you can post the goods movement for
the delivery.

Procedure for System Administrators

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.