Sending data via AJAX request

[eluser]Unknown[/eluser]
Hello,
I'm unable to send data to controller via AJAX request. I have this code:

Code:

$.ajax({
                type: "POST",
                    url: "controller/method",
                    dataType: "html",
                    data: ({'key' : 'value'}),
                    success: function( data ) {
                        alert( data );
                    }
                });

Ajax response handler throws error code 500 and no data are returned.
It works fine when making request without additional data (parameter data).

Any idea?

Thank you.