How long have you waited? (before concluding that it's frozen)
If I remember correctly, avast! browses the drive's folders until the place it stopped the last time is found - and it resumes scanning from there. During this initial browsing, the "initializing" message is displayed. So, if you have lots of files/folders on your disk and stopped in a "wrong" place last time, it might take a while before the continuation is found. Or, maybe if the recent last folder was deleted...
I know, there are a few things to improve here