I've just determined using Firebug that when Fancybox window is created it actually takes all of my ASP.NET controls (contained in DIV tag) and puts them outside FORM tag. So I guess this is the reason why then ASP.NET button doesn't do anything - it is placed outside form.
So, do you have any suggestions how I can prevent this (or make that ASP.NET button work), other than using completely different modal dialog?
Thanks in advance.
EDIT: The only good answer we have so far is not working for everybody (me included), so please help out if you have solution.