ST server reports:
"I Server 31/Jun/07, 12:12:12 Rejecting Server 192.168.0.3 - reported security level=0"
1. This is usually mismatched VP_Security_Level in sametime.ini.
2. Also verify servers can see each of the other servers via port 1516.
Simply "telnet otherserver.mydomain.com 1516" and verify connection is made. Alternately, use NotesPing/NotesConnect if available.
3. If error is with older 3.x or 6.5x ST server, awareness issues can be addressed by implementing the parameter VP_SECURITY_LEVEL=0 in the sametime.ini. See Technote: 1159885 - "Sametime 6.5.1: Errors Occur when Sametime 6.5.1 Interacts with Sametime 2.x/3.x Server with Critical Fix 1 Applied".
4. See also Technote: 1206752 for more information on ST / Sametime connectivity between servers for Awareness.