Exception &1 for reading languages for index category &2

What causes this issue?

An error occurred when defining the existing language indexes for the
relevant index category.

System Response

Exceptions:
1:
Unknown index category ID (CATID_UNKNOWN)
2:
Index category is deactivated (IDXCAT_IS_INACTIVE)
3:
XERROR

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

Error message extract from SAP system. Copyright SAP SE.