Today, I have added new AjaxControlToolkit controls to Velodoc pages and I got exception “Extender controls may not be registered before PreRender” from running a page.
All our pages derive from our own WebPage class which derive from the standard Page class. WebPage provides features like custom error handling and QueryString parsing into page properties.
The page where we had the new extender control had the following method:
protected override void OnPreRender(EventArgs e)
//The following line is required, otherwise you get "Extender controls
//may not be registered before PreRender."
//Some code that displays errors on postbacks
The solution to the problem above is to add base.OnPreRender(e); at the beginning of the method.