Based on the provided code snippets I have indicated several possible reasons that may lead to the experienced behavior.
When using RadAjaxManagerProxy in a content or control page you should place an instance or RadAjaxManager on the master page. In our online help this is more thoroughly explained.
Also have in mind that adding Meta tags in your master page should be within the <head> tag.
In our online demo
An alternative approach of using ModalBox
control would be using RadWindow
which is possible to be set as Modal. This will give you client side flexibility and ease of use.
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