I am having this same problem. I've read back a few pages in the forums and saw several people also with the same issue. I also used Norton before Avast!. I uninstalled it by following Symantec's very complicated uninstall directions from their website. Then installed Avist! and I still get the warning saying XP can't find an antivirus program.
I'd appreciate any help if someone has fixed this before.
Thanks
Can you boot in Safe Mode and try to repair your avast installation?
Boot while pressing the F8 key.
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove
Then choose Repair function in the popup window (Repair).
You must be connected to the internet while repairing.
If you can't make it work, please, post the contents of the C:\WINDOWS\system32\config.NT file.
Also, post the contents of these Windows Registry keys in your system?
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers\\VDD
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\VirtualDeviceDrivers\\VDD
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Control\VirtualDeviceDrivers\\VDD
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\Control\VirtualDeviceDrivers\\VDD
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet004\Control\VirtualDeviceDrivers\\VDD