There is a VMware connect timeout value relating to VMware Policies that you can increase in the Administration Console under View > Options.. Policies tab
Some comments say increase to 300 or try smaller increments first.
Mainly though target your VCB Proxy server and create debug log directory
..\NetBackup\logs\bpVMutil
In here is the results of the query to the ESX host or VirtualCenter.
Furthermore make sure your Administration Console is at the latest version as it updates the Virtual Machine dialog box with some options to refresh the list of VM's or to just reread the previous list obtained.
I was at 6.5.0 Admin Console, my Master at 6.5.1, once i updated my PC to 6.5.1 this dialog appeared, give you more choices, than go out every time.
And this is what this debug log above is capturing. It is running the VCB executable 'vcbvmname' on the proxy. Which you can run manually also.
Be careful if on a 64 bit OS, or see some of my other posts, I have just updated to 6.5.2 and it has cleared all my issues with VCB backups while on ESX3.5