Ah right, what you are wanting to do is backup your VM's. This is best done using VCB backups. You will need backup software like CommVault or similar to act as a proxy server to perform the backups.
http://vmzare.wordpress.com/2007/03/05/vcb-backup-strategies/This will give you some information on what VCB is.
The way you are trying to do it is very unreliable and should not be used as a method of backup.
Hope this helps.