exception please help

hi all, i am new to the forum and also new to c# and windows forms.i am trying to develop a windows form which can download multiple zip files by taking URL and filename as input from user. but getting an exception, Exception detail, System.Reflection.TargetInvocationException was unhandled Message="Exception has been thrown by the target of an invocation." Source="mscorlib" StackTrace: at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Delegate.DynamicInvokeImpl(Object[] args) at System.Windows.Forms.Control.InvokeMarshaledCallbackDo(ThreadMethodEntry tme) at System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(Object obj) at System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Windows.Forms.Control.InvokeMarshaledCallback(ThreadMethodEntry tme) at System.Windows.Forms.Control.InvokeMarshaledCallbacks() at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg) at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData) at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.Run(Form mainForm) at downloadmanager.Program.Main() in C:\winformsexp\downloadmanager\downloadmanager\Program.cs:line 17 at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() The source code, using System; using System.Threading; using System.IO; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms; using System.Net; using FolderZipper; using System.Collections; namespace downloadmanager { public partial class DownloadManagerForm : Form { int i = 0; List wc = new List(); List dwnprogress = new List(); List dwnpercentage = new List(); List dwnfile = new List(); public DownloadManagerForm() { InitializeComponent(); } private void Form1_Load(object sender, EventArgs e) { } private void Downloadbutton_Click(object sender, EventArgs e) { string[] remoteUri =new string[20]; remoteUri[i]= URLtextBox.Text; string[] fileName = new string[20]; fileName[i]= FileNametextBox.Text; string[] myStringWebResource = new string[20]; string[] mysrcpath = new string[20]; //mysrcpath[i]= Application.StartupPath + "\\" + fileName; char[] separator ={ '.' }; string[] dir = fileName[i].Split(separator); string mydestinationpath = Application.StartupPath + "\\" + dir[0]; if (i == 0) { Label downloadingfiles = new Label(); downloadingfiles.Text = "Downloading Files"; downloadingfiles.Left = 191; downloadingfiles.Top = 230; this.Controls.Add(downloadingfiles); } wc.Add(new WebClient()); wc[i].DownloadFileCompleted += new AsyncCompletedEventHandler(Completed); wc[i].DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged); // Concatenate the domain with the Web resource filename. myStringWebResource[i] = remoteUri[i] + fileName[i]; wc[i].BaseAddress = ""; //progressBar1.Visible = true; //label1.Text = fileName; dwnprogress.Add(new ProgressBar()); dwnprogress[i].Left = 108; dwnprogress[i].Top = this.Size.Height + 30; dwnpercentage.Add( new Label()); dwnpercentage[i].Left = 2; dwnpercentage[i].Top = this.Size.Height + 37; dwnfile.Add( new Label()); dwnfile[i].Text = fileName[i] + "//n" + remoteUri[i]; dwnfile[i].Left = 108; dwnfile[i].Top = dwnprogress[i].Top - 4; this.Controls.Add(dwnpercentage[i]); this.Controls.Add(dwnprogress[i]); this.Controls.Add(dwnfile[i]); wc[i].DownloadFileAsync(new Uri(myStringWebResource[i]), fileName[i]); i++; //ZipUtil.ZipFiles("C:\\Documents and Settings\\user1\\Desktop\\tower", "tower", ""); //Directory.CreateDirectory(mydestinationpath); //ZipUtil.UnZipFiles(mysrcpath, mydestinationpath, " } private void ProgressChanged(object sender, DownloadProgressChangedEventArgs e) { dwnprogress[i].Value = e.ProgressPercentage; dwnpercentage[i].Text = e.ProgressPercentage.ToString() + "%"; } private void Completed(object sender, AsyncCompletedEventArgs e) { dwnprogress[i].Visible = false; dwnpercentage[i].Text += " Download completed!"; MessageBox.Show("Download completed!"); } } } please do help.i would be very thankful for u.