FacebookError exception in android

I am trying to integrate Facebook login with my android application but whenever I try to login "FacebookError" method is invoked. Can anyone plz tell me what's causing it and how to handle it? I am using Facebook sdk version 3.23.1.

Here is my code:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);



    //connect=(Button)findViewById(R.id.authButton);
    button=(ImageView)findViewById(R.id.connect);
    button.setOnClickListener(this);
    updateButtonImage();
}

private void updateButtonImage() {
    if(fb.isSessionValid())
    {
        button.setImageResource(R.drawable.logout);
    }
    else
    {
        button.setImageResource(R.drawable.login);
    }
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

@Override
public void onClick(View v) {
    if(fb.isSessionValid())
    {
        //button close our session, log out of facebook
        try {
            fb.logout(getApplicationContext());
            updateButtonImage();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    else
    {
        //login to facebook

        fb.authorize(MainActivity.this, new Facebook.DialogListener() {
            @Override
            public void onComplete(Bundle values) {
                updateButtonImage();
            }

            @Override
            public void onFacebookError(FacebookError e) {
                Toast.makeText(MainActivity.this, "FbError", Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onError(DialogError e) {
                Toast.makeText(MainActivity.this, "OnError", Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onCancel() {
                Toast.makeText(MainActivity.this, "OnCancel", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{
    super.onActivityResult(requestCode, resultCode, data);
    fb.authorizeCallback(requestCode, resultCode, data);
}

}