This is referance to a thread that was closed with no resolution:
When I go to run a scan on my Vista machine I get the following error: "Could not start scan. Scan engine return error 0x20000003."
I had the same problem and was able to fix it. I checked services and Symatic was not started eventhough is was set to automatice start and when I tried to start I received an error. Then I remembered that I had another antivirus program (AVG Anti-virus free edition) installed. So, I deleted AVG Anti-virus and after the manadatory reboot. Symantec worked just fine. Anti-virus programs don't play well together. So if you have any other anti-virus programs loaded try uninstalling it.