c#代码中的错误

下面是MSDN的例程。但当我将运行它时，它却报错。
在  MethodInfo m = assem.GetType("Example").GetMethod("SampleMethod");
一行出现“未处理NullReferenceException”的错误

请问，是什么原因？应该怎样解决？
谢谢

using System;
using System.Configuration;
using System.Security.Permissions;
using System.Reflection;

namespace ConsoleApplication1
{

    [assembly: AssemblyVersionAttribute("1.0.2000.0")]

    public class Example
    {
        private int factor;
        public Example(int f)
        {
            factor = f;
        }

        public int SampleMethod(int x)
        {
            Console.WriteLine("\nExample.SampleMethod({0}) executes.", x);
            return x * factor;
        }

        public static void Main()
        {
            Assembly assem = Assembly.GetExecutingAssembly();

            Console.WriteLine("Assembly Full Name:");
            Console.WriteLine(assem.FullName);

            // The AssemblyName type can be used to parse the full name.
            AssemblyName assemName = assem.GetName();
            Console.WriteLine("\nName: {0}", assemName.Name);
            Console.WriteLine("Version: {0}.{1}",
                assemName.Version.Major, assemName.Version.Minor);

            Console.WriteLine("\nAssembly CodeBase:");
            Console.WriteLine(assem.CodeBase);

            // Create an object from the assembly, passing in the correct number
            // and type of arguments for the constructor.
            Object o = assem.CreateInstance("Example", false,
                BindingFlags.ExactBinding,
                null, new Object[] { 2 }, null, null);

                // Make a late-bound call to an instance method of the object.
            MethodInfo m = assem.GetType("Example").GetMethod("SampleMethod");     // 错误的地方

            Object ret = m.Invoke(o, new Object[] { 42 });
            Console.WriteLine("SampleMethod returned {0}.", ret);
            Console.WriteLine("\nAssembly entry point:");
            Console.WriteLine(assem.EntryPoint);
            Console.ReadLine();
        }
    }


}

--------------------编程问答-------------------- MethodInfo m = assem.GetType("Example").GetMethod("SampleMethod");
检查assem.GetType("Example")是否得到，然后GetMethod是否得到，肯定是没有得到，访问了空对象 --------------------编程问答-------------------- assem.GetType("Example").GetMethod("SampleMethod");

assem=null或者assem.GetType("Example")=null --------------------编程问答-------------------- MethodInfo m = assem.GetType("color=#FF0000]ConsoleApplication1.[[/color]Example").GetMethod("SampleMethod");
要带命名空间 --------------------编程问答-------------------- MethodInfo m = assem.GetType("ConsoleApplication1.Example").GetMethod("SampleMethod");

补充：.NET技术 ,  C#