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.

• Wait for the first installation to end, then start the second one.
• If you cannot locate the currently running installer, rebooting the machine may help.

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.

• If you need to automate this in a wrapper, you can check if there’s an installation in progress and wait for it to end. Check for msiexec /i or msiexec /x or msiexec /<something> using pv.
• (Not recommended) If you think that the installation in progress is hanging and should be stopped (or something similar), you can try to end it by killing the running msiexec.exe instances.
• (Not recommended) Reboot the machine. This will kill any installation in progress. Then try again.
• InstallSite mentions three extra solutions to the problem. If the solutions above haven't solved the issue, you might check the InstallSite.