It means that your Registry Keys:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\VirtualDeviceDrivers
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\Control\VirtualDeviceDrivers
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers

have errors… probably a wrong driver is listed there.
I suggest you post here what is written on that keys using, if you can, Registrar Lite (http://www.resplendence.com/reglite). Hope this help.

Did you install any other antivirus before avast? Specially, did you use NAV?