[jQuery] Can't Get Data Back from $.ajax() Call in IE7?

[Vik]

I've been testing this past few weeks in IE7, and I've got one
specific case where $.getJSON() seems to call the server
intermittently, and usually not at all. I use $.getJSON() a lot.  In
FF and Safari it always works, and even in IE7 it usually seems to
work, but not in this case for some reason.  I've tried setting cache
to false:

$.ajaxSetup({
                cache: false
        });

...but that doesn't seem to have fixed it yet.

So now I'm trying plain $.ajax() instead of $.getJSON:

        $.ajax({
                url: "/myFunction?type=json",
                cache: false,
                mode: "sync",
                data:
                        {
                                theDataToCheck:theDataToCheck,
                                GramsOrML: GramsOrML,
                                UnitCount: UnitCount,
                                UnitsOfMeasurement: UnitsOfMeasurement,
                                
LetOtherPeopleUseThisInfo:LetOtherPeopleUseThisInfo,
                                ajax_call: 'true'
                        },
                dataType: "jsonp",
                success: function(data) {
                                //handle data
                                //data comes back undefined in IE7
                }
        });


This always sends the call to the server, so I'm part of the way there
towards fixing this bug.  However, although this $.ajax() call always
works in FireFox and Safari, in IE7, the data seems to come back
undefined. Here's the skeleton of the PHP code:

                $JasonCallBack = $_REQUEST['callback'];

                //put return data in $theData array

                $S = $this->json->encode($theData);

                $S = $JasonCallBack . '(' . $S . ');';

                echo $S;

What can I do to get the data variable to be decoded properly in my
$.ajax() call in IE7?