I faced this error when i was rebuilding and index online but without the online the index rebuilds fine.
This is caused by Bug:2525767. The online rebuild of the index creates a journal table and index and the table contains more columns in its index with total length greater than number reported in ORA-01450 error message.This is a feature of online rebuild.
Maximum key length is calculated with respect to the database block size. It
means that current value of the initialization parameter db_block_size is not
large enough so that the internal journal IOT can be created without errors.
Workaround to rebuild the index offline.