problem with NetServerEnum

[Bhoot]

Inorder to list all the workstations on a LAN, i have used NetServerEnum() after importing it.

On running the program, it seemed to work fine. The two existing machines were detected correctly.
However, i want the list to be refreshed whenever required (some refresh button). So i detached the wire of the other computer from the switch, rendering only a single computer on the LAN.
Now, when i ran the program, it still lists out the disconnected machine.

How to solve this out?

The code is as follows :

namespace LanIpAddresses
{
	class NetApi
	{
		[DllImport ( "Netapi32.dll", EntryPoint = "NetServerEnum" )]
		public static extern Int32 NetServerEnum (
			[MarshalAs (UnmanagedType.LPWStr)] String serverName,
			Int32 level,
			out IntPtr bufferPtr,
			UInt32 prefMaxLen,
			ref Int32 entriesRead,
			ref Int32 totalEntries,
			UInt32 serverType,
			[MarshalAs (UnmanagedType.LPWStr)] String domain,
			IntPtr handle );

		[DllImport ( "Netapi32.dll", EntryPoint = "NetApiBufferFree" )]
		public static extern UInt32 NetApiBufferFree ( IntPtr buffer );
	}


	class EnumerateLanMachines
	{
		public const UInt32 SUCCESS = 0;
		public const UInt32 FAIL = 234;
		public const UInt32 MAX_PREFERRED_LENGTH = 0xFFFFFFFF;
		//public ArrayList machines = new ArrayList ( );

		enum ServerTypes : uint
		{
			WorkStation = 0x00000001,
			Server = 0x00000002
		}

		[StructLayout ( LayoutKind.Sequential, CharSet = CharSet.Auto )]
		public struct MachineInfo
		{
			[MarshalAs ( UnmanagedType.U4 )]
			public UInt32 platformId;

			[MarshalAs ( UnmanagedType.LPWStr )]
			public String serverName;
		}

		public enum Platform
		{ 
            PLATFORM_ID_DOS = 300,
            PLATFORM_ID_OS2 = 400,
            PLATFORM_ID_NT = 500,
            PLATFORM_ID_OSF = 600,
            PLATFORM_ID_VMS = 700
		}

		public void enumerateMachines ( )
		{ 
			IntPtr buffer = new IntPtr();
			int totalEntries = 0;
			int entriesRead = 0;
			int result;

			result = NetApi.NetServerEnum ( null, 100, out buffer, MAX_PREFERRED_LENGTH, ref entriesRead, ref totalEntries, (uint) ServerTypes.WorkStation, null, IntPtr.Zero );

			MachineInfo machineInfo;

			if (result != FAIL)
			{
				Console.WriteLine ( "Succeeded!" );
				Console.WriteLine ( entriesRead );
				for (int i = 0; i < entriesRead; ++i)
				{
					machineInfo = (MachineInfo) Marshal.PtrToStructure ( buffer, typeof ( MachineInfo ) );

					//machines.Add ( machineInfo );
					Console.WriteLine ( machineInfo.serverName );

					buffer = (IntPtr) ( (ulong) buffer + (ulong) Marshal.SizeOf ( machineInfo ) );
				}

				NetApi.NetApiBufferFree ( buffer );
			}
		}
	}
}

namespace LanIpAddresses
{
	class Program
	{
		private static IPHostEntry ipHost;
		static ArrayList ipList;

		static void Main ( string[ ] args )
		{
			EnumerateLanMachines enumerate = new EnumerateLanMachines ( );

			enumerate.enumerateMachines ( );

			/*foreach (EnumerateLanMachines.MachineInfo o in enumerate.machines)
			{
				Console.WriteLine ( o.platformId + " " + o.serverName );
			}*/

			Console.ReadLine ( );
		}
	}
}