No conversion possible between unit of measure for product &1 and unit &2

What causes this issue?

Unit of measure &V2& has been entered in TLB profile &V3&. The base
unit of measure for product &V1& can however not be converted to unit
&V2&.

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?

Change TLB profile &V3&, or the alternative units of measure in the
product master data for product &V1&.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.