checkboxlist

Please, help!    I'd like to change checkboxlist items programmaticaly, but this code doesn't work:

Sub ClickImg(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.ImageMapEventArgs) 
        Dim item As ListItem
        For Each item In CheckBoxList1.Items
            If item.Value = e.PostBackValue Then
                If Not item.Selected Then
                    item.Selected = True
                Else 
                     ...