I thought that (like I always do) you have to remove that specific screen from /usr/share/enigma2 and reboot the box? After the reboot you see the emergency skin and you can select a skin that will work.
To get back you need to login to your box via the terminal with putty or get on your box with ftp or smb or so... (just type in the browser \\ip.from.your.box)... find the file /etc/enigma2/settings and remove the line that defines the skin.