Summary: How to fix the Installation Error 1618.
Related installation help: Troubleshooting Rhino 5 Installation
The log file shows “Error 1618. Another installation is already in progress.”
The meaning of an exit value of 1618 of msiexec is ERROR_INSTALL_ALREADY_RUNNING. It’s one of the most common codes of Windows Installer. This happens if an installation started while another one was already running. There cannot be two instances of msiexec running at the same time.
If you can not locate an installer that is running it may be a Windows update or video or other driver update (like a Bootcamp driver, for example). In this case, proceeded with the Manual Install as detailed on the 1603 Error in Step #4. Step #1 Windows Updates is also important to have complete and completed without errors.
Why can a manual install help? The manual install recognizes installer that is already running and cancels them for you with your permission, so the Rhino installer can be run.