Hi all,
If you are having problems with installing the patcher on Windows, please go to your control center / programs and functions menu, right-click on HALion 5 and select “repair” before installing the 5.1 update.
I have deleted the previous post by lxegs that recommended to edit the registry since we recommend to use the repair function. Many thanks to lxegs though for figuring out an alternative way to solve the problem.