Error while drop user
When i have tried to drop ACC user i got fllowing error
SQL>DROP USER ACC CACSADE;
drop user acc
ERROR at line 1:
ORA-01001: invalid cursor
ORA-00600: internal error code, arguments: [qmxiUnpPacked2], , , , ,
, , 
After getting this error i have checked than there is no object in ACC user.
ORA-600 [qmxiUnpPacked2] [121 being reported during a drop user on a new 18.104.22.168 database.
This is generally caused by an invalid upgrade from earlier release.
If a database is created with the DBCA at 22.214.171.124 and one of the "seed" databases are used (not the "New Database" option),
then this seed database is at 126.96.36.199.
Once the create database is complete it needs patching to 188.8.131.52
This error occurs due to XMLType data that has not been successfully upgraded from a previous version.
To implement the solution, please execute the following steps:
1)SQL> shutdown immediate
2)SQL> startup migrate
3)SQL> spool patch.log
5)SQL> spool off
I follow the steps as mention by you.
My problem is solved