This problem is almost always exactly what it says - disk space.
Are you quiescing by any chance?
Are you using the latest ghetto script?
I am cloning 35 VMs a night from several 5.x ESXi without problems so there is no flaw in ghetto for me.
Is it possible you do a 3 rotation? Try changing to 2 or 1 rotation.
The thick to thin can be a trap also because some storage systems report the size differently.