DavidR
12
Sorry but resident AVs load low level drivers so that they can do their task of intercepting calls to files so that they can be scanned before being allowed to be run. These drivers can clash in the same way as dogs fighting over one bone.
The fact that you haven’t had problems in the past is a happy coincidence.
Since avast 9 is a major upgrade things have changed so conflict is a possibility rather than the fact that you didn’t have problems with two AVs installed…
If you aren’t prepared to even entertain that possibility and remove the other AV to test the theory, then there isn’t a great deal more that anyone can suggest.