We recently upgraded from 12.0 to 12.1.  All systems updated with the exception of a Windows 2000 Server that is a member of the Windows 2008 SBE Premium domain.  When I push the files to install 12.1, 12.0 re-installs.

Is 12.1 compatible with Windows Server 2000?

Not supported , I do not see it listed here.ONly these are supported

• Windows XP Home or Professional (32-bit, SP2 or later; 64-bit, all SPs)
• Windows XP Embedded
• Windows Vista (32-bit, 64-bit)
• Windows 7 (32-bit, 64-bit, RTM and SP1)
• Windows Server 2003 (32-bit, 64-bit, R2, SP1 or later)
• Windows Server 2008 (32-bit, 64-bit, R2, SP1, and SP2)
• Windows Small Business Server 2008 (64-bit)
• Windows Small Business Server 2011 (64-bit)
• Windows Essential Business Server 2008 (64-bit)
• Mac OS X 10.5 or 10.6 (32-bit, 64-bit)
• Mac OS X Server 10.5 or 10.6 (32-bit, 64-bit)

System Requirements for Symantec Endpoint Protection, Enterprise and Small Business Editions, and Network Access Control 12.1

http://www.symantec.com/business/support/index?page=content&id=TECH163806

Hi,

It is not supported.

Check this article

http://www.symantec.com/docs/TECH163806

However article says clients before version 12.1 can be managed by this version of the Symantec Endpoint Protection Manager, regardless of the client operating system.

So I would suggest install SEP 12.0 client on Windows 2000 machines and replace Sylink.xml.

SEP 12.1 will managed those SEP 12.0 clients, let me know the result.

I hope it will work for you.