ORA-00031: session marked for kill

Today, i was trying to kill a session as explained in
http://rakeshocp.blogspot.com/2009/04/kill-session.html but i was getting error "ORA-00031: session marked for kill" i got to know that we need to kill an OS session then. I wanted to kill "hassan's" session.
select spid, osuser, s.program from v$process p, v$session s where p.addr=s.paddr;
SPID OSUSER PROGRAM
------------ ------------------------------ ----------------
4844 rakesh.kumar
7168 rakesh.kumar plsqldev.exe
6012 Hassan plsqldev.exe


C:\Documents and Settings\Administrator>orakill icpora 6012
Kill of thread id 6012 in instance icpora successfully signalled.
C:\Documents and Settings\Administrator>

Thanks to the Don Burleson
http://www.dba-oracle.com/t_kill_process_windows.htm