After I configured replication and let it run for a few times, I tested the failover scenario with two different Windows 2008 server (one SP2, the other R2). The replicas seemed to start without a problem, but were unreachable. After inspection I discovered that the virtual NIC wasn't connected and forcing a connect resulted in an "Invalid configuration for device '0'" error

1: Remove the NIC from the guest (using Virtual Machine Properties)
2: Add the NIC again but uncheck connect at power on (the guest will hang if you forget this)
3: Start the guest and wait until the login prompt
4: Force connection
5: It works

The funny thing is that it will not only work, but the newly added NIC will even have the settings of the original one.
BTW, the reason that I found this so quickly was that the same thing happened when I tried to run a VM that I moved from an ESXi host on an ESX host. And then, I didn't find this solution so soon

Ideas anyone?
Jan