I think this is a bug, maybe a corner case. I am running VMPro on Centos in a virtual machine using Centos-Xen. I made a new virtual machine, set up the fqdn and so on and then installed VM GPL, hoping to be able to move my domains one at a time to the new VM and then switch to my Pro license. So I ran a backup using webmin on the Pro machine. This amounted to about 600-odd megs of data. Then I logged in to the new (destination) machine and made a new virtual server with the same name as that on the Pro server and ftp'd the backup file over and did a restore. That worked fine. I could not get access to the new machine until I had changed the DNS records to the IP address of the new virtual machine. Then I discovered that the new machine would not serve pages because apache wasn't running. Logging in to the ip address on port 10000 as root worked and showed me that apache was not running. I could not start it and could not get a comprehensible error message about why. I tried this from the command line as well as from the VM GUI. It may well be that I did not know where or in what log file to look for an error message. The thread here will partly detail what I did.
I found when trying to ftp from the old (Pro) virtual machine to the new (GPL) machine that my put command on apachemod.pl failed with an error that I COULD figure out. I was told that I was out of space on the new machine. Didn't seem likely but sure enough when I checked there was the backup file (all 600 megs) sitting there alongside the restored site (also 600 megs) putting me over the 1Gig default limit. So I immediately allocated another gig of quota and rebooted the virtual machine. But following Eric's advice to remove the analytics option and then re-enable it had no effect. In the end I typed in the text of the perl file and made it executable and that seems to have made everything hunky-dory.
BUT this solution does not scale well and is quite unexpected. You'll see from locutus' remark that the behaviour obtains under reasonable circumstances but is undesirable. So it would be nice if I didn't have that particular problem to worry about, I'd like to get on with moving my other domains.