Change your Java security settings to Medium (this is the lowest it will go, much like drink sizes at a movie theater)
If you're using Windows you can find this in the Control Panel under Java
Thank you for the post.
FileMaker Inc. is aware of this issue and our Testing and Development departments are currently investigating. At this time, our recommendation is to leave the Java security level at high, but add http://localhost:16000 in as an exception.
For FileMaker Server 12, the recommended version of Java is 7 update 71. For more information, please review the following knowledge base articles: