How do I fix the problem

Imports System.Net
Imports System.IO
Public Class downloader
    Private WithEvents downloadclint As New WebClient
    Dim Filename, Path As String
    Private Sub Downloaded(sendar As Object, ByVal e As System.Net.DownloadDataCompletedEventArgs) Handles downloadclint.DownloadFileCompleted
        Process.Start(Path & "\" & Filename)
    End Sub
    Private Sub StopBut_Click(sender As Object, e As EventArgs) Handles DownloadBut.Click
        AddHandler time.Tick, AddressOf tik
        AddHandler downloadclint.DownloadProgressChanged, AddressOf Changsize
        AddHandler downloadclint.DownloadFileCompleted, AddressOf Downloaded
        time.Enabled = True : time.Interval = 1
        If DownloadBut.Text = "Stop" Then
            DownloadBut.Text = "Start"
            If MsgBox("Are You Sure ?", MsgBoxStyle.Exclamation + MsgBoxStyle.YesNo) = MsgBoxResult.Yes Then downloadclint.CancelAsync()
        ElseIf TextBox1.Text.StartsWith("http://") Or TextBox1.Text.StartsWith("https://") Then
1:
            FBD.ShowDialog()
            If FBD.SelectedPath <> "" Then
                Path = FBD.SelectedPath
            Else
                MsgBox("Select Your Path")
                GoTo 1
            End If
            Dim spliter As String() = Split(TextBox1.Text.Trim, "/", , CompareMethod.Text) : Filename = spliter(UBound(spliter))
            Try
                downloadclint.DownloadFileAsync(New Uri(TextBox1.Text.Trim), Path & "\" & Filename)
            Catch ex As Exception
                MsgBox(ex)
            End Try
            TextBox1.Text = ""
            DownloadBut.Text = "Stop"
        Else
            MsgBox("insert Real Address")
            TextBox1.Text = ""
        End If
    End Sub

Exception has been thrown by the target of an invocation.
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart()
mscorlib.dll!System.Delegate.DynamicInvokeImpl(object[] args)
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbackDo(System.Windows.Forms.Control.ThreadMethodEntry tme)
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(object obj)
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state)
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallback(System.Windows.Forms.Control.ThreadMethodEntry tme)
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbacks()
System.Windows.Forms.dll!System.Windows.Forms.Control.WndProc(ref System.Windows.Forms.Message m)
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.OnMessage(ref System.Windows.Forms.Message m)
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.WndProc(ref System.Windows.Forms.Message m)
System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.DebuggableCallback(System.IntPtr hWnd, int msg, System.IntPtr wparam, System.IntPtr lparam)
[Native to Managed Transition]
[Managed to Native Transition]
System.Windows.Forms.dll!System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(System.IntPtr dwComponentID, int reason, int pvLoopData)
System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(int reason, System.Windows.Forms.ApplicationContext context)
System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoop(int reason, System.Windows.Forms.ApplicationContext context)
System.Windows.Forms.dll!System.Windows.Forms.Application.Run(System.Windows.Forms.ApplicationContext context)
Microsoft.VisualBasic.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
Microsoft.VisualBasic.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
Microsoft.VisualBasic.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(string[] commandLine)
[Native to Managed Transition]
[Managed to Native Transition]
mscorlib.dll!System.AppDomain.ExecuteAssembly(string assemblyFile, System.Security.Policy.Evidence assemblySecurity, string[] args)
Microsoft.VisualStudio.HostingProcess.Utilities.dll!Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart_Context(object state)
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx)
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state)
[Native to Managed Transition]