Upgrade to version 6 database configuration screen does not appear. Instead the following appears. Have tried complete reinstall of VM and several restarts of Tomcat/Apache in varying sequences.
Service Temporarily Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.
Can you please connect to the Virtual Appliance admin console, press U to upgrade and follow the prompts. It seems that the LiveTime install within that particular version of the VM is corrupted. The upgrade process will replace it with a new one (in fact I believe it will update you to 6.0.4).
This should solve your current problem.