Variable &3 not defined

What causes this issue?

Variable &V3& specified in the variable assignment for conditional rule
&V1& (call number &V2&) is not defined.

System Response

The attribute normalizing rule is inconsistent and 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

Correct the rule.

Error message extract from SAP system. Copyright SAP SE.