When trying to uninstall Royal Server you get the error message:

"The setup must update files or services that cannot be updated while the system is running. If you choose to continue, a reboot will be required to complete the setup."

This will happen shortly after installing Royal Server only. It is due to the fact that the MSI packet of Royal Server is doing .net optimisations (ngen) after the installation in the background that has not been finished yet. 

Wait, until the ngen process is done (shown as ".NET Runtime Optimization Service" in the Task Manager.