Since a recent update of OSX, there's an issue with the Java-plugin not being active, even though Java Control Panel says it is. This is because in Safari the plugin is still set to inactive.
To resolve, surf with Safari to www.java.com/nl/download/testjava.jsp. You see the Java website with in the center the notification that the plugin is not active. Click on the text to re-active the plugin.
Send a link to this post to yourself or a friend.