Condition table &1 was activated with a warning

What causes this issue?

Condition table &v1& was activated with a warning.
A condition table is a database table. It can only be activated if it is
in a consistent state.

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?

Refer to the activation log messages output after this message. They
describe the cause of the activation problem in detail.
Note: Table conversions in conditon tables can cause problems if the
table is already being used productively.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.