i bought the s4u mirror plugin for sketchup a while a go and installed it on the computers i use for modelling. i’ve replaced one of the machines and uninstalled sketchup but i can not install the plugin on the new machine with the warehouse manager reporting a license limit exceeded.
If you don’t have the old computer to uninstall it from, I think you’ll need to keep trying to get in touch with the author to see if he can reset the license for you.