Ajax calls

Hey guys
I am struggling to get data from Piwik using APi JSON method.

	$.getJSON('http://demo.piwik.org/?module=API&method=VisitsSummary.get&idSite=1&period=day&date=today&format=JSON&token_auth=anonymous', function(data) 
				 alert (data);

The request is made but I always get empty data (null).
I tried with all other methods but its always teh same.

Furthermore, using firebug I can see that request returns 200, and when i click on the link on which request has been made i can see the data…

So I am kin dof lost on this one. Any help will be greatly appreciated.