I suggest you trash Norton. It started going downhill the day Peter stopped writing the code, and Symantec only makes it worse every year.
In fact, Symantec products are banned from any of my systems. I actually fired a client who insisted on using Symantec on her office network. If I'm going to support the network and be the one who has to respond to outbreaks, then I am also the one who gets to decide what security software will be used. My solution of choice is Trend Micro Office Scan (or Trend Micro Internet Security for machines not on a domain).
But AVG is a VERY close second.
Now as far as conflict, having two virus scanners is a very big no-no, for several reasons. One is that they sometimes attack each others' definitions. The other is that all virus scanners have a lot of things in common in terms of how they interface with the system to protect the computer, and having multiple programs trying to do the same thing simply doesn't work.
I think the problem you're experiencing is the result of a conflict between AVG and Norton; and no, simply disabling Norton is not enough to be sure that the conflict is rectified. There are browser objects and virtual drivers involved.
My suggestion is that you completely uninstall Norton (preferably along with anything else Symantec makes, which you can do by using the Norton Removal Tool, if Norton refuses to uninstall cleanly in the usual way).
Then reboot and run Crap Cleaner, including the registry cleaner ("Issues"), which will clean up all the crap that the Norton uninstaller leaves behind. Make a backup when prompted, then let it fix all issues. Then reboot again.
Next, completely uninstall AVG, reboot, run Crap Cleaner again, and reboot again.
I don't recall the last time a Norton installation uninstalled cleanly; I think it may have been this century, but I'm not positive.
So there may be other traces of Norton left behind that can be removed with HijackThis. But it's a dangerous program if you don't know how to use it. If you decide to try, just look for anything in there that says "Norton" or "Symantec," and leave everything else alone unless you know
exactly what you are doing. Otherwise, skip this step.
Next, reinstall AVG.
Good luck!
-Rich