Class type & : transaction not allowed

What causes this issue?

Class type &V1& was defined such that classification transactions
cannot be started. To classify the object, you can only use object
maintenance functionality.

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?

Call the maintenance function for the object, then classify the object
in the maintenance function.

Error message extract from SAP system. Copyright SAP SE.