As I tried to install Fixpack 2 for Lotus Notes 8.5.1 today the installation failed with the message “Error encountered while installing Notes Core Hotfix component.”.
After some investigation I found that the JQS.EXE process (Java Quick Starter) seems to conflict with the installer (or has one of the Notes processes in use, although I cannot explain why).
As soon as I killed JQS.EXE with the Windows task manager the installation succeeded. Maybe this will help others with the same issue …