I tried to repair the install without resorting to a new installation but it wouldn't go. Then I tried to reinstall. That didn't work either. Then I panicked.
Searching the internet for the exact error message that appeared I found that it had something to do with a messed up installation of Microsoft Framework dot Net. That must have happened with yesterdays Automatic updates. I'm really starting to get fed up with microsoft automatic updates! This reminds me of Excel 2003.. after a Microsoft update it suddenly would not open Lotus spreadsheets anymore. Now if I want to open a Lotus file I first need to go to Control Panel -> software and deinstall the latest security update for Microsoft Excel. Every time, because the damn stubborn idiot thing keeps reinstalling the stoopid update after I've turned my back. I've tried to switch that off, so now it doesn't give me the option any more, it just goes ahead without asking. Obviously I can't be trusted with making important decisions. Heh.
Long story short (believe me, you don't want to know how long exactly) I tried to remove the Framework dot Net versions but initially couldn't, then searched around, read other peoples reports of the same problem, followed other other peoples advice for solutions, and finally succeeded in cleaning up and reinstalling the offensive programs, and then reinstalling Autocad. That took the whole day, from 10AM to 8PM.
In between I had time to clean the superkids room and chase away some spiders nesting in the dust. I found out that contrary to what I have always thought, Rinke (the superkid) is really a very organized person. He even has a filing cabinet with labelled boxes. Which is lucky for him. Because I was armed with a very big garbage bag and a very bad mood. This label was the only thing standing between his precious belongings and the incinerator.
Label: "Spy fyle box - Rinke".
("spionnen docee doos" -> docee = "dossier")