It could be a number of conflicts. Just because it works well on someones desktop doesn't mean it will on my laptop. The time I used Comodo firewall and avast, I still had the issue with slower web browsing and slower start up. It clearly must be something else that is causing the conflict. What is the conflict? I'm not really sure. As I said there are plenty of free Av's out there that don't have the same conflicts. As joeblack mentioned his combo seems to be working fine for him.