Lesson: Backup machine certificates before upgrading View Composer
When upgrading a View environment, the first place to start is View Composer. In a recent upgrade to Horizon 6 the upgrade of Composer failed with Error 1920, shown below:
It did not take long to find this VMware KB article which then pointed to his Microsoft KB article. The error occurs in environments that do not have Internet connectivity and cannot connect to the appropriate URLs for checking certificate trust lists. Microsoft provides a patch and a policy setting to resolve the issue. The fix was simple enough. Upon implementing the fixes provided by Microsoft the installation was restarted. When reaching the step in the installation where the certificate is to be selected, it was found that the machine certificate for this system was removed. There is no explanation for this certificate removal. The two places this was seen was in a lab environment, where certificates were easy to redeploy, and an environment that was using self-signed certificates. This is why it is always a good idea to backup certificates before upgrading View Composer, or any operation for that matter.