The runat=server attribute is definitely required, as this indicates that the button control is an ASP.Net Control, and will be treated as such when the page is parsed by the ASP.Net engine. Without it, the button will not function.
Yep, I know. That's why I suggested he could try changing the <asp:Button> control with the <input> tag. I have the exact problem with JavaScript recently. I keep on reviewing and re-typing my script but I still found no errors, the function won't execute. Changing the ASP.NET control to a HTML tag solves it since I don't need any server side scripts.