The unit field & is not unique

What causes this issue?

Field group &V2& should have been processed internally in &V3&.
However, the field group cannot be processed because unit &V1& for this
field group is not the same for all senders and receivers.

System Response

A error is processed because there is no alternative field group than
&V2& to use. Posting &V3& is therefore no longer possible.

How to fix this error?

Determine whether you really want to update &V2& to &V3&. If this is
necessary, ensure that all senders and receivers use the same unit.

Error message extract from SAP system. Copyright SAP SE.