Overlay image - "Destination Host Unreachable"



we have a debian 7.0 server which hosts a VM. In this VM we have another debain 7.0 server which runs OpenERP and a PostgreSQL database together with it.
We have chosen to run this in a VM because we want to use overlay images every time we update or add new funtctionality to the OpenERP (openerp.com) for testing purpose. Once everything runs as it should we want to merge the overlay into the main image.
Open ERP is used through a webbrowser over the internal network.

First test confront us with the problem that we can not access the OpenERP once we run the overlay image. From inside of this VM it seems that OpenERP is running and logfiles confirm that. IT is just not reachable from outside. Also pining this server (has a static IP adresse) results in a Destination Host Unreachable

Any hints on how to get over this? …many thanks …Serge