Comment 8 for bug 562189

Yay! That did it! I added a --hostname and it just worked, so thanks very much.
I don't think it's to do with whether a VM already exists as I have none in my folder and have been wiping /tmp files between each build (because it doesn't clean up after dying). In my case it should have nothing to clash with as I'd never had a successful build before! It's curious that the lack of a hostname should provoke an overwrite check when the --dest param deals with where the VM will be put.
I'll report it as a documentation bug as well since the official docs on using vmbuilder don't even mention the hostname property: http://doc.ubuntu.com/ubuntu/serverguide/C/jeos-and-vmbuilder.html