Adding an Activity in Android Studio causes app to have Unexpected Error?

I am creating an app which when pressing a button causes it to go to a new activity/window. However I keep getting an unexpected error every time I try this.

The following is part of the error from logcat:

06-21 10:42:13.232 22991-22991/edu.cmu.sphinx.pocketsphinx E/AndroidRuntime: FATAL EXCEPTION: main
    Process: edu.cmu.sphinx.pocketsphinx, PID: 22991
    java.lang.IllegalStateException: Could not execute method for android:onClick
    at android.view.View$DeclaredOnClickListener.onClick(View.java:4458)
    at android.view.View.performClick(View.java:5204)
    at edu.cmu.pocketsphinx.demo.Gvoice$2.run(Gvoice.java:108)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:148)

The following is part of the java code which works except the W4 window which keep giving the error:

public void onButtonClick(View v) {
    if (v.getId() == R.id.BHome) {
        String str = a1.getText().toString();


        //Go to the relevant page if any part of the phrase or word entered in the 'EditText' field contains 'xxx' which is not case sensitive
        if (str.toLowerCase().contains("home")) {
            Intent userintent = new Intent(Gvoice.this, PocketSphinxActivity.class);
            startActivity(userintent);
        } else if (str.toLowerCase().contains("W1")) {
            Intent userintent = new Intent(Gvoice.this, W1.class);
            startActivity(userintent);
        } else if (str.toLowerCase().contains("W2")) {
            Intent userintent = new Intent(Gvoice.this, W2.class);
            startActivity(userintent);
        } else if (str.toLowerCase().contains("W3")) {
            Intent userintent = new Intent(Gvoice.this, W3.class);
            startActivity(userintent);
        } else if (str.toLowerCase().contains("W4")) {
            Intent userintent = new Intent(Gvoice.this, W4.class);
            startActivity(userintent);
        } else {
            Toast.makeText(getApplicationContext(), "Incorrect Information", Toast.LENGTH_SHORT).show();
        }
    }
}

If anyone knows where I should look that will be greatly appreciated