Fedora 12 and Ubuntu 14, right?
I feel like you and @Scott-B know each other? https://forums.fogproject.org/topic/5306/adding-needed-repository-failed
It’s likely possible to upgrade 1.2.0 from node to full server. There will be issues, but Ubuntu 14 shouldn’t be too much trouble.
The path, generally, would be to delete the existing settings file from the previous node installation, then just run the 1.2.0 installer and choose normal installation. You’d also have to update option 066 (the next-server) on whatever is running DHCP. If you want to maintain control of your FOG Client service running in your environment, you’d leave DHCP alone and go through the task of changing the storage node’s IP address to the old FOG server’s. Once the web UI is running, you’d then have to correct all of the storage node stuff from the old DB. You would also need to correct the image definitions for every image - which would probably mean deleting (not the image, the definition) and then recreating every one. The image paths are case sensitive and the OS and image type and paths must exactly match what the image actually is.
However, moving to something like Fedora 21 or 22 and migrating the DB and images isn’t too tough, and I’d be willing to help out with this should you need it. And, if you’re going to go through the trouble of what’s said above… it might be easier to just rebuild and migrate.