Upgrading my Ubuntu installation killed my nx setup (to be more correct, it started by killing my entire setup). As nomachine only distributes 32 bit versions of their stuff, you have to make a bit of an effort to get stuff running…
Download the client, node and (free) server from nomachine, the from the directory where these can be found, as root, run
apt-get install ia32libs dpkg -i --force-architecture nxclient_2.1.0-17_i386.deb dpkg -i --force-architecture nxnode_2.1.0-22_i386.deb dpkg -i --force-architecture nxserver_2.1.0-22_i386.deb dpkg -i ia32libs /usr/NX/bin/nxserver --useradd name /usr/NX/bin/nxserver --usercheck name /usr/NX/bin/nxserver --start
That should be all. The names of the downloaded files may need fixing to match your version. The name which is given should be an existing user on your system. Once, this is done, you should be able to login to the system using your nx client.