Be sure that your Avast! Add-In in Outlook 2007 is activated.
Open Outlook, extras, open "Vertrauensstellungscenter - sorry, don`t know the English origin -, add-ins, left side below you can see a scroll-box, open "exchange clientmanagement, click go to and a window should be open - see below.
I have had never problems with this avast! plugin. It works for me like expected, simply perfect
Hope, i could help.
Tevion