Just tried executing ashsimp2.exe which gives me the very same behavior. When I run it the first time I get the spinning waiting circle in Vista and then nothing more happens and Avast! never starts but when running it next time Avast! starts right away and then it starts just fine every time I run the ashsimp2.exe file - it's only the very first time I get this strange problem with Avast! not starting (or at least not showing the user interface).
No, I haven't had any other AV program installed and this Vista installation is also a very fresh installation with all MS security updates etc.
When I uninstalled Avast! trying to get rid of this problem I first uninstalled it the normal way using the Program and Features under Control Panel and then I also manually deleted everything related to Alwil/Avast! in the Registry and I did the same on a file level making sure there were no left-overs and then I finally rebooted my computer before installing Avast! again and I also downloaded the latest setup file from Avast.com.
This isn't really a big problem, just feels a bit annoying and strange why you need to run Avast! two times whenever you want to use it...