Error & when generating index & to table &

What causes this issue?

Error in index generation

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?

Check the entries in tables IA<DBS> and IG<DBS> where <DBS> stands for
the database system you are using.

Error message extract from SAP system. Copyright SAP SE.