Stefano & Smallbox
IIUC OP has just updated his SME8, not upgraded from 7 to 8
Well Smallbox does not clearly say ie
"Today I upgrade my SME Server 8 beta 5....."
As OP wants to downgrade to 7, then it seemed likely that the upgrade to 8 had been made from sme7.5.1
Smallbox, did you upgrade from sme7.5.1 or upgrade from an earlier sme8 version ?
Either way you should still lodge a bug.
I think I recall a bug about NICs being not identified correctly, so search bugzilla first.
You do not say why you cannot run "Configure this server" , because that would be the obvious thing to do. If you do not have network access due to NIC issues, then login as admin directly at the server console.