Rule &2 has no fixed unit of measure, but variable &3 is not filled

What causes this issue?

In basic rule type &V1&, basic rule &V2& does not have a fixed target
unit of measure. However, variable &V3& is not filled.

System Response

The basic rule cannot be executed.

How to fix this error?

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

Procedure for System Administrators

The assigned field in the object to be normalized does not contain a
unit of measure and therefore cannot be normalized. Check the binding of
the corresponding attribute normalization rule and the object fields or
use a fixed unit of measure where possible.

Error message extract from SAP system. Copyright SAP SE.