Indexes to non-transparent tables are deleted

What causes this issue?

Secondary indexes were defined for a nontransparent table.

System Response

It makes no sense to define secondary indexes for transparent tables.
The index definition is therefore deleted in the ABAP Dictionary.

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.

Error message extract from SAP system. Copyright SAP SE.