vSphere Update Manager: Database temporarily unavailable or has network problems.

I have just installed the vSphere Update Manager on my vCenter server (running version 6.5) and when I click the Update Manager tab in the vSPhere Web Client I get this message:

Database temporarily unavailable or has network problems.

Cause:
Database temporarily unavailable or has network problems.

I have used the vSphere Update Manager Utility (located in D:\Program Files\VMware\Infrastructure\Update Manager) to check the settings and re-initialize the database to no avail.

Next I looked in C:\ProgramData\VMware\VMware Update Manager\Logs and opened the VMware-vum-server-log4cpp.txt file – in here I found the following lines:

[SQL Server]Login failed for user ‘MYDOMAIN\VC-SERVER$’

This suggested that the service is running under the Local System context so now I have changed the service to run as a service account (one that has access to the SQL database) the problem has gone away and I can use Update Manager.