For Panda files detected as being infected:
That is a know issue. Panda refuses to encrypt their signatures
(INFO)Make sure you are logged in as administrator (not as user with admin rights) while trying to remove the registry keys. Also make sure there is no process/application running that can use those keys.
Make sure everything from NAV is gone. add/remove is not enough. For versions up to 2003 there is a standalone util to remove it on Symantec's website. Link to it can be found on this board. For versions 2004 and up, you have to do it manully as explained on Symantec's website. Link to it is also somewhere on this board.
To repair Avast:
start > control panel > add/remove > Avast > change/remove > (scroll down) repair.