Hi
You can try this Solution
Before Doing any changes in the Registry
Take the Backup of the Registry
Eventhough this document mentions vista os,it worked for me in Windows 7
Installation Issue Document:
http://service1.symantec.com/support/ent-security.nsf/854fa02b4f5013678825731a007d06af/5c45f3798fdd78e3492575d7001f71c3?OpenDocument
Don't use Single Exe,better use bunch of Files ie MSI Package
First Install Liveupdate followed by Symantec Antivirus.msi,if you are going to use for Managed Environment,while creating the package,create bunch of Files Package.
When you click on Export on the Left Hand Side top Uncheck the Option Create a Single Exe for the package.Better use Unattended as the Installation Type,also you may face pending system changes in Windows 7
For pending system Changes Delete the pending File Rename Operation key from Registry
Package Creation Document:
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007110513361348
Pending System Changes Document
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007121609023348
Hope this will work for you