The Kit SE is part of Groove Agent 5 SE, which is part of the Cubase 10 and Nuendo 10 series of products (I can’t remember whether all versions of Cubase 10 get The Kit SE). It will not work if you only have a Cubase 9.5 licence. Is it, perhaps, a leftover from a Cubase 10 trial? If so, you probably want to remove Groove Agent 5 SE (using your system’s uninstall feature) and The Kit SE (using Steinberg Library Manager).
The other option is to upgrade to Cubase 10 or Nuendo 10. All retail versions of Cubase 10 is on 50% off sale at the moment, including version upgrades. (Education pricing is not discounted, but 50% off retail pricing is cheaper than education pricing anyway).