I am writing a core service to publish the entire pages in a structure group. I have written a recursive method to get all pages in a structure group.

I am loading all pages in a list and publishing them.

I am able to get all pages in a list, but unable to publish them.

My entire code is here.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Tridion.ContentManager.CoreService.Client;
using System.Xml.Linq;
namespace CoreServiceApp
{
    class Program
    {
        static int countPage = 0;
        static List<string> pageArray = new List<string>();
        static void Main(string[] args)
        {
            SessionAwareCoreServiceClient client = new SessionAwareCoreServiceClient("netTcp_2011");
            //get the structure group TCM ID
            Console.Write("Enter TCMID of structure Group:");
            string structureGroupTcmID = Console.ReadLine();
            String targetTcmId = "tcm:0-70-65538";
            Program prog = new Program();
            //Call the recursive method to get all pages in structure group
            prog.PagePublish(structureGroupTcmID, client);
            PublishInstructionData pubData = new PublishInstructionData();
            //convert the pages to string
            string[] pages = pageArray.ToArray();
            //publish
            try
            {
                client.Publish(pages, pubData, new[] { targetTcmId }, PublishPriority.Low, new ReadOptions());
            }
            catch (Exception ex)
            {
                Console.WriteLine("Publish: Unable to publish Page"+ex.StackTrace, ex);
            }
            Console.WriteLine("Total No of Pages" + pages.Length);
            client.Close();
        }

        private void PagePublish(string tcmID, SessionAwareCoreServiceClient client)
        {
            ReadOptions readOptions = new ReadOptions();
            OrganizationalItemItemsFilterData filter = new OrganizationalItemItemsFilterData();
            var elements = client.GetListXml(tcmID, filter);
            foreach (var element in elements.Elements())
            {
               String pageCheck= element.Attribute("ID").Value;
               String specID = pageCheck.Substring(pageCheck.LastIndexOf('-') + 1, 1);
                //check for structure group
                //If structure group call method again
               if (String.Equals(specID, "4"))
               {
                   PagePublish(pageCheck, client);
               }
               //its page
               else
               {
                   pageArray.Add(pageCheck);
               }

            }
          
        }
    }
}

I am getting error while publishing.

The exception is

Publish: Unable to publish Page
Server stack trace:
   at System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRunt
ime operation, ProxyRpc& rpc)
   at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean on
eway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan tim
eout)
   at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCall
Message methodCall, ProxyOperationRuntime operation)
   at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)

Exception rethrown at [0]:
   at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage req
Msg, IMessage retMsg)
   at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgDa
ta, Int32 type)
   at Tridion.ContentManager.CoreService.Client.ISessionAwareCoreService.Publish
(String[] ids, PublishInstructionData publishInstruction, String[] targets, Null
able`1 priority, ReadOptions readOptions)
   at Tridion.ContentManager.CoreService.Client.SessionAwareCoreServiceClient.Pu
blish(String[] ids, PublishInstructionData publishInstruction, String[] targets,
 Nullable`1 priority, ReadOptions readOptions)
   at CoreServiceApp.Program.Main(String[] args) in H:\Documents\Visual Studio 2
010\Projects\PagePublish\PagePublish\Program.cs:line 28
Total No of Pages2

And the exception message is

Value cannot be null.
Parameter name: publishInstruction.ResolveInstruction.

Please let me know is there any better way to do this and fix to resolve the exception.