sorensenjeppe,

  1. avast features quite a thorough check for competitive AV software, and warns the user accordingly. It didnt’ obviously work in your case, though – what version of Norton are you using, exactly? Is there a file called navrt.sys or savrt.sys somewhere on your system disk?

  2. did you consider removing NAV instead of avast?

Anyway, this is not only a problem with avast. Virtually any two AV programs don’t work together… (and epecially with Norton AV)

Thanks
Vlk