|It is not rare for AV programs to conflict with whatever else you have onboard. I'm using MSE and have no trouble at all (now I've fixed a long standing issue on my machine).|
Don't have more than one AV running. Avast seems to work fine on most machines, then there is always AVG as already mentioned.
All of the above are free and I've found little incentive to go for the pay-for versions of the last two on a home machine.
Ms Hulot goes horse riding