Hi all, i REALLY need help with this

I'm using a simple AJAX call using XmlHttpRequestObject:
However, eventhough i'm setting the 'asynch' parameter of the 'open' function to 'true', the call is made synchronously!!!
I checked it by using delays in the server, and the browser hangs (all other operations that are after the call to 'send').
the code:
xmlHttpObj.open("POST",url,true);
xmlHttpObj.onreadystatechange = function() { ...}
xmlHttpObj.send(null);
and I'm using IE 7.
How can this be



Help!
Thanks!