SQL> drop user HR cascade;
drop user HR cascade
*
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-00942: table or view does not exist
------解决方法--------------------------------------------------------
Cause:An error occurred while processing a recursive SQL statement (a statement applying to internal dictionary tables).

在运行一条递归SQL语句(该语句将应用于对内部表或数据字典的操作)时，发生错误。这样的错误好头疼啊.楼主可以先drop该用户下的所有对象，然后在drop这个空用户.

------解决方法--------------------------------------------------------
Create a synonym for SDO_GEOM_METADATA_TABLE under sys which points to
MDSYS.SDO_GEOM_METADATA_TABLE