It has come to my attention that there's a problem with the installation in certain cases. I have investigated this for a few hours and come down to this:
If you have Microsoft .NET Framework 4 installed you are not affected.
Otherwise the Click Once system will download it for you after you clicked that "Accept" button when you were asked to accept Microsoft's license for the .NET Framework. It then installed the framework and proceeded to ask you if you want to install Stoffi. When you clicked "Install" it started to download Stoffi, but then it failed and gave you an error dialog.
However, if you just close that last error dialog and then start setup.exe again it works!
I am not really sure what the cause of this is but it looks like it could be something with the manifest file, perhaps a security related problem. I will try to fix it as soon as possible!
However, trying to make up for that mistake I have released an upgrade with a few bugfixes for you. I have fixed bug #1, #2, #3 and #4.