Please see http://www.avast.com/forum/index.php?board=2;action=display;threadid=1179 .

We have an update available (not official but working). You can download it from

http://cat.asw.cz/~vlk/ashOutXt.dll

just replace the file with that name in your avast directory with this new one, and you should be all set (first shut Outlook as otherwise the files will be locked).

Vlk