The graphics devices enumerated with a call to GraphicsEnvironment.getScreenDevices() may contain some "ghost", or "invalid" devices (those not existant at the moment). This happens on MS Windows: the devices array contains devices for monitors that have once been attached to the system, but are in no way active at the time when the application is starting or running.

The problem is reported at: http://forums.java.net/jive/thread.jspa?messageID=483902