due to security restriction, can not access type system.runtime.remoting.objref

Question

due to security restriction, can not access type system.runtime.remoting.objref

After running example Chapter04\Sponsor of book distributed .net programming in c#

got error

due to security restriction, can not access type system.runtime.remoting.objref
at leaseInfo.Register(new CustomerClientSponsor());
static void Main(string[] args)
      {
         // Load the configuration file
         RemotingConfiguration.Configure("MathClient.exe.config");
         Customer cust = new Customer("Homer Simpson");
         
         // Register the client side sponsor
         ILease leaseInfo = (ILease)cust.GetLifetimeService();
         leaseInfo.Register(new CustomerClientSponsor());
         // Loop until user enters "q" to quit
         Console.WriteLine("Enter 'q' to quit: ");       
         do
         {
            Console.WriteLine("Server returns: {0}", cust.SayHello());
         }while (Console.ReadLine() != "q");
      }
 class CustomerClientSponsor : MarshalByRefObject, ISponsor
   {
      private int mRenewCount = 0;
      
      // Implements ISponsor.Renewal
      public TimeSpan Renewal(ILease leaseInfo)
      {
         if (mRenewCount < 3)
         {
            mRenewCount++;
            // Just a trace messsage for testing.
            Console.WriteLine("CustomerClientSponsor.Renewal()");
            return TimeSpan.FromSeconds(5);
         } 
         else 
         {
            // Just a trace messsage for testing.
            Console.WriteLine("CustomerClientSponsor.Renewal(), returning 0 time!");
            return TimeSpan.FromSeconds(0);
         }
      }
   }