I have parallels 12 and kept getting the prompt to install Toolbox. I eventually did. It now says "Your license key is invalid for this version of Parallels Toolbox. Please downgrade or buy a new license. If you want to annoy users with prompts, the least you can do is to install the correct version. It's not that hard is it?
Hello Michael Sargent, Please quit Parallels Toolbox (click on the Parallels Toolbox icon in the Mac menu bar, then on the cogwheel icon in the upper right corner within the application interface, select 'Quit Parallels Toolbox' from the menu that appears), remove Parallels Toolbox (refer to https://kb.parallels.com/123905 for assistance), reboot the Mac, download Parallels Toolbox from - http://download.parallels.com/toolbox/v2/2.0.2-1213/ParallelsToolbox-2.0.2-1213.dmg -, install it and activate it.