"Unfortunately, <App Name> has stopped." Common unexplained Error

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http://stackoverflow.com – I am having a problem when debugging apps that respond to user input. An ordinary app that just displays text works fine, but when I give a button an event handler I get a generic message "Unfortunately, 'App Name' has stopped.". I have tried many solutions, but to no avail. I am using IntelliJ IDEA 12.0.4 (Community Edition). Sorry for asking a very common question but it seems the solution is different for everyone. Source Code: package com.example.Android_Test; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.wi (HowTos)