Assignment to '&1' invalidates previous assignment to '&2'

What causes this issue?

The expression &V1& addresses a data object that was already accessed
using the expression &V2&. The previous expression has filled a sub-
component with a value. This subcomponent is now overwritten by the
assignment. The assignment made is invalidated as a result.

System Response

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

How to fix this error?

Remove one of the two assignments, or, if the assignment is part of the
subcomponent, swap the order of the assignments.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.