From the stack trace, it seems like his method commandAction in class Traffic is trying to create a new instance of class 'subscribe', which extends MIDlet.
In general, you may not create instances of classes extending MIDlet: that's the job of the phone's
Java VM (actually, its application manager). If you try, you'll correctly get a security exception.
Since this MIDlet subclass called 'subscribe' is not actually being used here as a MIDlet (i.e. a thing the user can run, managed by the application manager), move the functionality needed from it here into a separate non-MIDlet class, then create an instance of that instead.