A proccess is getting the following error when execute a query;
ORA-00600: internal error code, arguments: , [hash aggregation can’t be done], , , , , , 
Look for this error at MOS, I can see it is a bug. (if you have access to Support refer note 729447.1). It recommend upgrade until fixed version or apply two workaround, putting disable for all database or our session with;
alter system set “_gby_hash_aggregation_enabled” = false;
alter session set “_gby_hash_aggregation_enabled” = false;
Other option is patch statement (or create an outline) using the next hint.
/*+ NO_USE_HASH_AGGREGATION */
HTH – Antonio NAVARRO