How to fix the error: “Extender controls may not be registered after prerender” when add multi user controls

ASP.Net questions are best asked in the ASP.Net Forum, wich is totally seperate from this one:

http://forums.asp.net/

But maybe the page-lyfecycle will make waht happesn a bit clearer (it's a very important thing to udnerstand in ASP):

http://ift.tt/KE9CLu

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Let's talk about MVVM: http://ift.tt/1fpEgna Please mark post as helpfull and answers respectively.