Using class in masterpage

Hi

I have a master page called basemasterpage which has a modalpopextender called mpuEmail

<asp:ContentPlaceHolder ID="mainContent" runat="server"><asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate><asp:Panel ID="emailPanel" runat="server"><uc:emailPopup ID="ucemailPopup" runat="server" /></asp:Panel></ContentTemplate></asp:UpdatePanel><cc1:ModalPopupExtender ID="mpuEmail" runat="server" PopupControlID="emailPanel" TargetControlID="btnHdn"></cc1:ModalPopupExtender><asp:Button ID="btnHdn" runat="server" Text="Button" Visible="false" /></asp:ContentPlaceHolder>

basemasterpage has a class in its code behind

Public Class MyMaster
    Inherits BaseMasterPage
    Public Sub ShowModal(showHide As String)
        If showHide = "Show" Then
            mpuEmail.Show()
        ElseIf showHide = "Hide" Then
            mpuEmail.Hide()
        End If
    End Sub

And in temp.aspx.vb i have the following sub

  Public Sub ShowModal(showhide As String)
        Dim masterPage As MyMaster = TryCast(Page.Master, MyMaster)
        masterPage.ShowModal(showhide)
    End Sub

Finally on a button click also in temp.aspx.vb, I have the following code

Protected Sub Button1_Click(sender As Object, e As EventArgs)
        ShowModal("Hide")


    End Sub

I get an object not set to an instance error on the masterPage.ShowModal(showhide)  line.

Any ideas?

Thank you so much i've been on this for hours.

Leonaisse