The following error message occurs
"Server certificate specified is unusable"
It is due to an incorrect installation of a certificate through the Microsoft management console (MMC), instead of the IIS installation wizard. This error occurring when assigning a certificate to a Citrix gateway.
If the pending request exists within the IIS installation wizard, delete the certificate installed through Microsoft management console (MMC) and install the certificate through the IIS installation wizard. Once installed, assign the new certificate to the Citrix gateway.
If not, delete the certificate installed through MMC