Thought you might want to look into this, since I'm pretty sure the current server the sandbox is using (whatever it is) is the cause of this. Hidden ASP.NET fields (ViewState, EventTarget, etc) are supposed to render inside a <div> tag. This is what the VS 2010 Development Server does. However, the same application hosted in this sandbox do not behave in this manner. The Hidden fields are there, but they are not rendered in a <div>, which means that any pages hosted in this sandbox will NOT validate as proper XHTML 1.1, as placing <input> as a direct child of <form> is not allowed under that doctype. I realize most developers don't care about stuff like that, but it's still wrong. Just FYI.