Don't think it is that simple. Having the same problem hen I tried AVG -- it wouldn't run either. I believe the problem goes deeper, but i'll try Panda if it will run at all on an old XP.
Thanks ES. I downloaded Panda and it is working fine. Have no idea what the problem was with the other antiviruses I tried, but I guess all is well that ends well and everything else appears to be working fine.