ORA-08104: this index object ##### is being online built or rebuilt

Hello,
If you have very busy database and you decide to run an online index rebuild, but unfortunately your session terminated abnormally or it becomes necessary to kill this session.  after that you are attempting to run the index rebuild again and is throwing the error : ORA-08104: this index object ##### is being online built or rebuilt
cause : A session failure during an online index rebuild can leave the data dictionary in a state reflecting a Rebuild is ongoing when in fact it is not.
solution :
Run dbms_repair.online_index_clean for fix this issue
declare
var1 BOOLEAN;
begin
var1 := dbms_repair.online_index_clean(#####);
end;
/

now you can run again online rebuild of index.