Killing sessions

Oracle 7.1.3 under solaris 2.4

How can I kill and oracle session. I tried svrmgrm, but sometimes I get a message "cannot.... session marked for kill". In situations like these I kill the unix process which seems to fix the problem. Still I wonder:

1. What trouble am I looking for, when I kill the unix process
2. Is there a cleaner way to kill a session ? -- Martin Drautzburg, Siemens Electrocom VOICE: 8636-18 (work), 69 99 18 (home); FAX: 8625-93 (work)