Did you do this from a fresh JB?
I tried this using both the com.nito.nitoTV package as well as the .deb that's available for DL from that link.
With the .deb file, it completely broke my installation and I needed to restore to factor settings and JB again.
With the com.nito.nitoTV package, it seemed to work however the screen was constantly flashing until I removed the com.plex.client-plugin
Seems like it'd be better to wait for ambertation.de to come back online
i restore to original os 4.2.1
then i jb with pwnage.
after that i install nitoTV via ssl@ip-apple-tv Terminal:
echo “deb http://awkwardtv.dyndns.tv ./” > /etc/apt/sources.list.d/awkwardtv.list
apt-get install com.nito.nitoTV
and then i do this installation