[PROBLEM] Upgrade to Beta troubles on usb install

[Jan]

Until tonight, I had a running usb install (following the guides, so there should be nothing special there). Basically I had mounted my usb drives partions to the right places using /etc/fstab.

Then I tried the upgrade like described on http://www.xbian.org/2013/07/xbian-1-0-beta-1-1-hotfix-for-xbian-1-0-beta-1/ Upgrading from XBian 1.0 Alpha 5

Everything downloaded without errors, the update installed, I got the new splash screen. But now, when I restart, I get welcomed by busybox telling me:

Terminal

Loading initram modules ...
Root partition LABEL=xbian-root-btrfs missing
mount: mounting LABEL=xbian-root-btrfs on /rootfs failed: No such file or directory

Now, I cannot even find /etc/fstab to check that. Whoami gives me an error (unknown uid 0), so I might not even be root.

How should I continue?