Pause/stop the Web Shield that will allow you to at least download it the avast file system shield may alert but have it take no action.
I have just downloaded it with this link http://oldtimer.geekstogo.com/OTL.exe web shield stopped and no alert by the File System Shield and I also did a scan of the and no alert, ensure that you have the latest virus definitions.
EDIT: just tried it again with the web shield running and no alert.