How do I display a modalpopupextender from a server side button click?

See more:

ASP.NET

Ajax

ModalPopUpExtender

I have an Ajax ModalPopUpExtender which works fine when launched by the target control, but what I want to do is launch it from a server side 'button_click' event.

This is because I want to check some variables before launching the ModalPopUpExtender.

I have tried the '.show' method which works fine on a 'PageLoad' event but the method won't work from an asp:button 'onclick' event.

I have given the ModalPopUpExtender a dummy button to target as you can't run one without the TargetControlID being set. The dummy control is visible.

As the '.show' method works on a 'PageLoad' event I know the ModalPopUpExtender is set up correctly, but what could be stopping it from running from a server-side event?

What I have tried:

<ajax:ModalPopupExtender
ID="mp1"
runat="server"
PopupControlID="Panel1"
TargetControlID="btnShowPopUp"																		CancelControlID="btnClose"
BackgroundCssClass="modalBackground">
</ajax:ModalPopupExtender>

Sub btnShow_Click(ByVal sender As Object, ByVal e As EventArgs)

       if myVariable = 1 then

          mp1.show

       End if

   End Sub