The other day I ran into a strange issue: When opening Lync Management Shell on one Front End, I was prompted to trust “Microsoft Corporation” as a Trusted issuer. Now, immediately this got me worried, although the certificate details looked legitimate. After some review, I chose the “Run once” option to see what happened next, only to be prompted over and over again. By now I got fed up and hit “Never run”. Bad mistake, as the Management Shell or import-module Lync in Powershell now would not work any more.
Rune's blog about things I see and UC 