I am using jquery 1.5.1

have this function 

2. function foo(section)
3. {
4.  $.post
5.  ( "/",
6.    { task: 'section',
7.      section: section
8.    },
9.    function(data)
10.    { 
11.      alert(data);
12.    }
13.  );
15. 
    

which works fine for every browser on every OS except IE 9 (9.0.8112.16421).

When the server returns an empty string, the popup pops up.

When the server returns something, nothing happens.

Any idea what the problem might be

Thank you