Recently seen this ORA-600 error at the time of opening the database.
Errors in file /u01/app/oracle/diag/rdbms/dbg/dbg02q/trace/dbg02q_ora_1802320.trc:
ORA-00600: internal error code, arguments: [krctcr_4], , , , , , , , , , , 
ORA-600 signalled during: ALTER DATABASE OPEN…
Mon Jul 18 07:42:08 2011
NOTE: Deferred communication with ASM instance
NOTE: deferred map free for map id 141
This error is caused by corrupt change tracking file. Solution is to disable the change tracking and re-enable it.
SQL> startup mount SQL> alter database disable block change tracking; SQL> alter database open;