如何解决未知实体错误？

Question

我在MainActivity.java中编写了以下代码，在android中创建了一个选项菜单：

package com.jain.ashutos;

import android.app.*;
import android.os.*;
import android.view.*;
import android.widget.*;
import android.content.*;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem; 
import android.widget.Toast;

public class MainActivity extends Activity
{
    /** Called when the activity is first created. */
@Override  
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
          setContentView(R.layout.main);
}

@Override 
public boolean onCreateOptionsMenu(Menu menu) 
{    
MenuInflater menuInflater = getMenuInflater(); 
menuInflater.inflate(R.layout.menus, menu); 
return true; 
}

@Override 
public boolean onOptionsItemSelected(MenuItem item) 
{

switch (item.getItemId()) 
{    


case R.id.menu_about:  
Toast.makeText(MenuSample.this, "You Clicked About", 
   3000).show();      
return true;
default: 
return super.onOptionsItemSelected(item);

            } 
       }
}

但是当我运行该程序时，我得到一个Error = Unknown Entity“MenuSample”。任何人都可以解决这个问题吗？