In order to get your custom dialogs to work you should register your script into the page when you make an AJAX request. This is done by using the ScriptManager
's methods for registering script inside an UpdatePanel control. Here you can find more information about this control and these methods specifically:
For your convenience I have attached your aspx page with the changes I made. In the button click event handler I register your script with the ScriptManager's RegisterClientScriptBlock
method. You can use it as a reference in your project.
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