To fix this problem open Avast and click "Real-Time Shields" from the left, then select "Behavior Shield" from the drop down menu, then on the right click on "Expert Settings", a new window will popup, click on "Trusted processes" on the right and copy and paste the path below into the "(enter process name)" bit
C:\Program Files (x86)\Origin Games\Battlefield 3\bf3.exe
After pasting the link, click "Add" at the bottom.
If you've installed BF3 into another folder you'll have to click browse and locate Battlefield 3\bf3.exe
Zkus tohle. Prý pomáhá.