Like many others here, I had one computer that reported 3035,2 errors with virus definitions missing or invalid on just about every reboot. Multiple uninstalls, NRTs, registry hacks, and support sessions failed to resolve it.
Thanks to a Microsoft update that created other problems on this computer, I was forced to reformat my hard drive and start from scratch.
After installing XP SP3, I thought that was a perfect opportunity to finally fix this !#$%& error. So I installed the downloaded NIS9 (16.2.0.7), hopeful that on reboot, that illusive green check mark would finally appear and stay. No such luck.
Checking the Event Log showed SRTSP failed to load with Event ID 7026. How is that possible? I just installed it on a virgin machine!!! !#$%&
So I started to do some digging. I looked in Documents and Settings for the Symantec files. Some seemed to be missing. Oh, I forgot that on a fresh install, the 'Show Hidden File and Folders' was not checked and 'Hide Protected Operating System Files' was. After changing that, there it was.
In the directory list, separate from my Documents and Settings folder was a DOCUME~1 folder. It was set-up just like the standard Documents and Settings folder, with All Users, etc. It was under this directory structure that I found the missing Symantec files.
So I tried to delete it. In use. A HA! I went in to Services, stopped Norton Internet Security, and successfully deleted this directory. Restarted the NIS service, did an Update in NIS, rebooted, crossed fingers and toes.
A green checkmark that has withstood 6 reboots over 12 hours.
For others with this error, I would be curious to know if this also resolved your issue.