求教：对一个命名空间的应用为何出错，谢谢！！！

Imports System.Windows.Forms
Imports Public Class B2
    Inherits Control
    Public Delegate Sub ItemSelectedEventHandler(e As HelperClasses.ItemSelectedEventArgs) ', e As CustomCollectionEditorForm.ItemSelectedEventArgs
    Public Event ItemSelected As ItemSelectedEventHandler
    Public Combo As New ComboBox()
       Protected Overrides Sub OnClick(e As EventArgs)
        MyBase.OnClick(e)
        RaiseEvent ItemSelected(New HelperClasses.ItemSelectedEventArgs(Combo.Items(0), 0))
    End Sub
End Class

Imports System.Drawing
Imports System.Collections
Imports Imports System.Windows.Forms
Imports System.Reflection
Imports Imports System.Data
'Imports CustomControls.Win32Controls
Imports CustomControls.Enumerations

'Namespace CustomControls.CollectionEditor

Public Class CustomCollectionEditorForm
    Inherits System.Windows.Forms.Form
    Private Combo As New ComboBox()
    ....
    ....

 Public Sub B21_ItemSelected(e As HelperClasses.ItemSelectedEventArgs) Handles B21.ItemSelected
        TreeView1.BeginUpdate()
        If Collection IsNot Nothing AndAlso e.SelectedItem IsNot Nothing Then
            Dim type As Type = DirectCast(e.SelectedItem, Type)
            Dim newCollItem As Object = CreateInstance(type)
            Dim newTItem As TItem = CreateTItem(newCollItem)
            Dim selTItem As TItem = DirectCast(TreeView1.SelectedNode, TItem)
                 TreeView1.Nodes.Add(newTItem)
            End If
            OnItemAdded(newCollItem)
            TreeView1.SelectedNode = newTItem
        End If
        TreeView1.EndUpdate()
    End Sub


 Private Sub Button5_Click(sender As Object, e As EventArgs) Handles Button5.Click

        TreeView1.BeginUpdate()

        If Collection IsNot Nothing Then
                            Dim type As Type = DirectCast(New HelperClasses.ItemSelectedEventArgs(Combo.Items(0), 0).SelectedItem, Type)

 Dim newCollItem As Object = CreateInstance(type)
            Dim newTItem As TItem = CreateTItem(newCollItem)
            Dim selTItem As TItem = DirectCast(TreeView1.SelectedNode, TItem)
                 TreeView1.Nodes.Add(newTItem)
            End If
            OnItemAdded(newCollItem)
            TreeView1.SelectedNode = newTItem
        End If
        TreeView1.EndUpdate()
    End Sub

Namespace HelperClasses
    Public Structure ItemSelectedEventArgs
        Private _SelectedItem As Object
        Private _SelectedIndex As Integer
        Public Sub New(SelectedItem As Object, SelectedIndex As Integer)
            Me._SelectedItem = SelectedItem
            Me._SelectedIndex = SelectedIndex
        End Sub
        Public ReadOnly Property SelectedIndex() As Integer
            Get
                Return _SelectedIndex
            End Get
        End Property

        Public ReadOnly Property SelectedItem() As Object
            Get
                Return _SelectedItem
            End Get
        End Property
    End Structure
End Namespace