Not likely to be anything to do with your NIC, as the errors are about X Windows failing to start up.
Rather than attempting to update the diskless image archive on your core. Why not just directly install the nVidia driver on the MD ... ie just update the bit you are interested in, rather than wholesale refresh all the system modules.
Delete the MD device and start again.... It will completely delete the /usr/pluto/diskless/<dev#> folder. Now boot the MD again to start the process. Once you have gotten to the "cycling" part again (make sure it is definitely complete in the setup).
From the core, type
(and your linuxmce password, then)
(where ## is the device number of the MD just created)
This will leave you at a root prompt for the MD, now you can install the nVidia driver. If it complains about X running or trying to run whilst you are installing the driver, you can always type at the MD -
To kill off all the higher level processes.
Once done, reboot. If there are still issues, then you need to review your /var/log/Xorg.0.log file for errors whilst X is starting up. You can also do this through the ssh shell, or directly on your core, here /usr/pluto/diskless/##/var/log/Xorg.0.log