I also was having this problem, but was able to finally get it working. As stated, you have to be running Java 7 or higher. The gotcha is if you install with Java 6, reinstalling it does not seem to work. So, if you installed it with Java 6, the steps to fix it are:
1) Upgrade Java to 7 or higher
2) Remove the packet filter plugin
3) Edit your database and drop the ofPfRules table
4) Delete the version for packet filter from the ofVersion table
5) Install packet filter
It should work after that, or it finally did for me. Hope it helps.