When setting up for the first time with Java Web Start the plugin, I get :
java.lang.NullPointerException
at org.hudson.trayapp.gui.tray.TrayIconImplementation.displayException(TrayIconImplementation.java:36)
at org.hudson.trayapp.model.Server.update(Server.java:98)
at org.hudson.trayapp.model.Server.<init>(Server.java:45)
at org.hudson.trayapp.model.Model.addServer(Model.java:65)
at org.hudson.trayapp.HudsonTrayApp.<init>(HudsonTrayApp.java:75)
at org.hudson.trayapp.HudsonTrayApp.getHudsonTrayAppInstance(HudsonTrayApp.java:47)
at org.hudson.trayapp.HudsonTrayApp.main(HudsonTrayApp.java:39)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.sun.javaws.Launcher.executeApplication(Unknown Source)
at com.sun.javaws.Launcher.executeMainClass(Unknown Source)
at com.sun.javaws.Launcher.doLaunchApp(Unknown Source)
at com.sun.javaws.Launcher.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

So, i'm not able to play with the Tray App plugin

Take care