While the following message can be caused by many reasons, I thought I’d list the one I encountered a few months back while deploying VUM.
There was an error connecting to VMware vCenter Update Manager - [serverName.domain.com: 8084].
Database temporarily unavailable or has network problems.
In my case, it was caused by service not running as the proper service account that has access to the database.
Once I changed the account to the proper service account that had access to the VUM database, the error message went away.