I am really sorry for your journey, @Lars_Blomstrand. I’ll talk to the SDA colleagues. Meanwhile I found another thread
It seems to be that your C:\Program Files\Steinberg\Install Assistant folder is damaged or not available. You can see that in your screenshot, too. Please check if the folder is there and rename it. Then create a new one. Does it work now?
Another suggestion is to change the download location in the SDA. To do this, please start the SDA and click to the “SETTINGS” icon. Now on left side change the folder of “Download Directory”.
Better now?
Michael.