[quote="Mappi75"]I cant install 11.7 on a clean Windows 8.1 Pro 64-Bit system:
there are serveral crashes during installation cant remember the messages in german language...[/quote]
First thing to check: Ensure the installer's digital signature is correct, in case it wasn't fully downloaded.
Other things to check: Problems installing Opus.
If none of those solve the problem, we will need to know the error messages and any other details you can provide.