When I click on the button I added I get the error (I put what I found pertinent) :

.com.apple.JarLauncher: Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at com.eteks.sweethome3d.swing.ControllerAction.actionPerformed(Unknown Source)

...

Caused by: java.lang.reflect.InvocationTargetException

...

Caused by: java.lang.NoClassDefFoundError: com/lowagie/text/Elementat com.eteks.sweethome3d.swing.MonitoringFrame.createSensorPagePanel(Unknown Source)

...

Caused by: java.lang.ClassNotFoundException: Class com.lowagie.text.Element
at com.eteks.sweethome3d.tools.ExtensionsClassLoader.findClass(Unknown Source)