This is what I got from their forums - "Resolution: the issue was a custom solution which was added to include Universal Search in toolbar. Once the dependant custom solution was uninstalled, user was able to uninstall Universal Search without
issue. This issue is considered resolved."
I suppose you need to uninstall some custom solution imported which was added while adding this to your organization. Once that has been uninstalled, you would be able to uninstall this solution.
Link:
https://community.sonomapartners.com/universalsearch/0540a8ae-0eb6-e411-b18b-00219b8d3233
Hope it helps!
Regards, Abhishek Bakshi If you find this post helpful then please Vote as Helpful and Mark As Answer. Check my blog on https://mydynamicscrmblog.wordpress.com/