Field name not allowed for purpose conditions

What causes this issue?

The current field name is defined as a Controlling object (part of an
organizational entity) and therefore cannot be used as a purpose
condition field.

System Response

Field name is not allowed for purpose conditions.

How to fix this error?

For the rule design, use the current field name as part of the data
controller. The other condition fields (not Controlling objects) can be
used as part of the purpose conditions.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.