when you upload the images to the datastore, then add the .vmx to the inventory, you start the simulator but realize that the network interfaces are not showing as connected.
when you try to tick the "connected" box and click OK, you get:
Reconfigure virtual machine:Incompatible device backing specified for device '0'.
Time: 12/03/2013 12:05:20
Target: sql2012-vsim-812-cm2
vCenter Server: ESCVC-AMS
Here is what you see from the vSphere client:

the only way out is to delete the network card from the VM and re-add them back (as E1000).
I thought I would share this with the next person who hits this.
Domenico