I attempted to install 11.0.5 but it abruptly stopped. Here was the output from the SEP_INST.log. This was the only output in the log.

=== Verbose logging started: 1/13/2010  7:50:38  Build type: SHIP UNICODE 3.01.4000.4042  Calling process: C:\WINDOWS\system32\msiexec.exe ===
MSI (c) (88:A8) [07:50:38:508]: Resetting cached policy values
MSI (c) (88:A8) [07:50:38:508]: Machine policy value 'Debug' is 0
MSI (c) (88:A8) [07:50:38:508]: ******* RunEngine:
           ******* Product: symantec antivirus.msi
           ******* Action:
           ******* CommandLine: **********
MSI (c) (88:A8) [07:50:38:508]: MainEngineThread is returning 1645
=== Verbose logging stopped: 1/13/2010  7:50:38 ===

Symantec Mail Security for Domino is currently installed already, not sure if that matters

I believe it's because I'm installing from a remote desktop client

which os you are trying to install?
win 7 vista?
try disabling uac

On Windows 2003 Server. I received and error code of 1645. I checked and it said

ERROR_INSTALL_REMOTE_PROHIBITED

1645

Windows Installer does not permit installation from a Remote Desktop Connection.

Please check this should resolve

Error message when you try to install a MSI package on a Windows Server 2003-based computer by using RDP connection: "Windows Installer does not permit installation from a Remote Desktop Connection"

http://support.microsoft.com/kb/927063

copy the file to locally and run the setup should be fine.

That's what I did and it installed perfectly

is that  endpoint 2010 antivirus will support windows 2003 server.

its not for server os
http://shop.symantecstore.com/store/symnahho/en_US/ContentTheme/ThemeID.1795800/pbPage.NAV10wide

SEPM will not install even if the package is local.