alter table add PARTITION ORA-14415 error

I have run this command

SQL>  alter table cw_tb_zvlist13 add PARTITION P_cvliste13_20160718

  2  values LESS THAN (TO_DATE('2016-07-19 00:00:00', 'SYYYY-MM-DD HH24:MI:SS', 'NLS_CALENDAR=GREGORIAN'))

  3  tablespace ts_cvliste13_20160718;

alter table cw_tb_zvlist13 add PARTITION P_cvliste13_20160718

             *

FEHLER in Zeile 1:

ORA-14415: Index in teilweise geloschtem Status, DROP INDEX weiterleiten

and get this error

but all indexes in the partions are valid and usable. I dont know why I get this error