Closing a TCP Asynch socket C#

I have a TCP socket application based on examples of asynch socket programming available on Microsoft site and an example on Code Project.  
My client is a GPRS based device which does not generally do a clean close on the TCP connection.   I need to remove these idle connections on my TCP server.  Am maintaining a hashtable in the server that keeps a record of the unique unitID sent by the client and the associated socket.  When the client reconnects -I need to course through the hashtable and close the socket related with the previous client ID and remove the entry in the hashtable and add this new entry with the current socket.  
My question is how to cleanly and surely remove a socket and how to manage the hashtable while doing so

My code is as follows

private bool removePrevSocketIfPresent(Hashtable hashTableUnits, long unitID)
        {
            bool allWEll = false;
            SocketAsyncEventArgs tempSocketToremove;
            DataHoldingUserToken tempTokenToRemove;
           //locking the hashtable for the whole operation
            lock (TRInitModule.hashTableUnits.SyncRoot)
            {
                bool markForRemoval = false;
                foreach (DictionaryEntry entry in TRInitModule.hashTableUnits)
                {
                    Int64 currentUnitID = Convert.ToInt64(entry.Key);
                    if (currentUnitID == unitID)
                    {
                        try
                        {
                            tempSocketToremove = (SocketAsyncEventArgs)(entry.Value);
                            tempTokenToRemove = (DataHoldingUserToken)tempSocketToremove.UserToken;
                            tempSocketToremove.SocketError = SocketError.OperationAborted;
                            tempSocketToremove.AcceptSocket.Shutdown(SocketShutdown.Both);

                            //is the above line enough or do I need to do the below lines too?
                           // tempSocketToremove.AcceptSocket.Close();
                           // tempTokenToRemove.Reset();
                            //if (tempTokenToRemove.theDataHolder.dataMessageReceived != null)
                            //{
                            //    tempTokenToRemove.CreateNewDataHolder();
                            //}
                         markForRemoval = true;
                            
                                Console.WriteLine();
                                Console.WriteLine("One socket removed, count is = " + TRInitModule.hashTableUnits.Keys.Count);
                            allWEll = true;
                        }
                        catch (Exception eRT)
                        {
                            allWEll = false;
                            Console.WriteLine("ERROR IN  REMOVE ITEM  " + eRT.Message);
                        }

                    }
                    else
                    {
                        markForRemoval = false;
                    }
                }
                if (markForRemoval)
                {
                    TRInitModule.hashTableUnits.Remove(unitID);
                }
            }
            return allWEll;
        }

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