system
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Huh, I’ve got a lot of replies to answer! 
Debugging: of course I can send a report. What I meant was that I don’t want to at the moment personally spend the time going through such a list. I don’t depend on XP anyway.
Installation: was a clean one with reboots between uninstallation and a new installation. I might give it another shoot using aswclean.exe if it could be that Avast doesn’t uninstall correctly.
Folders/installation target: All installations are done as new, I just follow my already memorized setup.
For the moment Avast is installed according to default settings, which works without any errors. If I decide to do another try this evening I report back to you. Let’s see it might be that it works the 6th time and I’ll be left with no clue what so ever!
Thanks for your help!