OntoGraf for visualizing ontologies in Protege does not start

I wanted to visualize an ontology with Protege. After a fresh installation of Protege (which btw does not work with openJDK out of the box) the bundled plugin for visualizing ontologies - OntoGraf - does not start.
1 answer

Installing Protege with needed requirement for OntoGraf on Linux Mint 12

There are some explanations for installing protege (with JDK 6 or later). But I ran into an additional problem when I tried to start the OntoGraf plugin.
If protege starts without problems (rename felix.jar or just use JDK 6 and not the latest version) but the OntoGraf plugin gives an error just install graphviz. On Linux Mint 12 you can run:
sudo apt-get install graphviz

Now the plugin works without further problems.