Have you recently tried requesting a certificate for your Lync environment from Comodo? If you used the Lync Certificate Wizard to generate the request, you will probably run into the same issue I did during a recent deployment - they will reject the request with a non-specific error. Why? There is currently a bug in their system that prevents them from processing the request if there are capital letters embedded in the CSR. The significance here is that when using the Lync Certificate Wizard to generate the CSR, it will maintain the case of the letters used within Topology Builder. Additionally, the Lyncdiscover and Lyncdiscoverinternal names that are automatically added through the wizard to the CSR have the first letter capitalized. Fortunately, we have a couple options to resolve this.