Client install EMPTY

http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2009042115381848

Nope, that didn;t work.  I am logged in as, and the install was run under, the domain Administrator username.

Any way once again you verify the permission for those registry keys. Also assure there is no Group policies are causing this problem .You can check the below discussion also.

https://www-secure.symantec.com/connect/forums/microsoft-software-restriction-policies

For diagnosing purpose you can use below tool also

http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2008071709480648

Try this,

Install the windows install clean up utility
Remove Symantec Endpoint Client
Do a clean install of the SEP client

Please update the status.

I also encountered the problem with SP3. Is there any conflcit with Win SP3?

I see this with xpsp2 also but I found that this is due to some threat inthe machine not detected by symantec.

filename: gphone.exe
machine: Machine
result: This file is detected as W32.Imaut.E.  

I repaired the antivirus and updated with latest rapid release
Virus definition detail:

Sequence Number: 101869 (or higher)

then it detected the threat. and after restarting al is ok now.

I had the same issue... I used cleanwipe and removed SEP. After reinstalling it started working.....