jQuery UI Autocomplete only works in IE on one machine - asp.net

Question

I've assembled a page as a proof-of-concept for retrieving matching user names from Active Directory (via a web service on out intranet) while typing values into a text box. It works beautifully, but only on my workstation and only in IE (version 10). Every other user who has tried it gets the alert, "error", which is also what I get when I try it in Chrome. I've further verified that the other users can actually retrieve the data by pasting the web service URL directly into their browsers, so the breakdown occurs somewhere between fetching the data and displaying in the form. My only thought was that maybe there are some browser settings responsible for allowing this to work, but I really have no idea what those might be.
Here's what the code looks like:
<div>
<h1>Active Directory lookup</h1>
<input name="txtADAccount" type="text" id="txtADAccount" style="width:400px;" />
</div>
</form>
<script src="http://ajax.aspnetcdn.com/ajax/jquery/jquery-1.8.0.js"></script>
<script src="http://ajax.aspnetcdn.com/ajax/jquery.ui/1.8.22/jquery-ui.js"></script>
<script type="text/javascript">
$(function () {
$("#txtADAccount").autocomplete({
source: function (request, response) {
$.support.cors = true;
$.ajax({
crossDomain: true,
headers: { 'Access-Control-Allow-Origin': '*' },
url: "http://fetch.mycompany.com/ADUser/ADUserByAccountOrDisplayName/" + $('#txtADAccount').val(),
dataType: "json",
contentType: "application/json; charset=utf-8",
dataFilter: function (data) { return data; },
success: function (data) {
var jsonData = JSON.parse(data);
// Filter out records where there is no email address
var jsonFiltered = jsonData.result.filter(function (row) {
if(row.mail != '') {
return true
} else {
return false;
}
});
response($.map(jsonFiltered, function (item) {
return { label: item.displayName + ' (' + item.mail + ')' }
}))
},
error: function (XMLHttpRequest, textStatus, errorThrown) {
alert(textStatus + ': ' + errorThrown);
}
});
},
select: function (event, ui) {
// prevent autocomplete from updating the textbox
event.preventDefault();
$(this).val(ui.item.label);
},
minLength: 2 //minLength as 2, it means when ever user enter 2 character in TextBox the AutoComplete method will fire and get its source data.
});
});
</script>
</body>
Just looking for some hints as to what the source of the problem might be.
UPDATE: Updating the script links to the latest versions of jquery and jquery.ui resulted in it working on at least one more workstation that didn't work previously. However, it's still not working on any other machines I've tried and the error messages displayed are not consistent. Sometimes it just displays "error", other times "error: No Transport", and other times "error: Access is Denied".
UPDATE 2: On this second workstation where I've been able to get it working, I noticed that if I log in using a different account, I get the "error: Access is denied" message. This is puzzling... to what exactly is access being denied? It's not the web service itself because any user can drop the web service URL into their browser and it will return the appropriate json data.
UPDATE 3: I just discovered that changing the contentType to "application/x-www-form-urlencoded; charset=utf-8" has resulted in it working now for several other users as well as working for me now in Chrome. It's still not working for at least two users, one using IE who gets no message whatsoever, and another who is still getting the "Access is denied" message (I may need to have them try clearing their browser cache). I'm still baffled as to why it always worked for me alone regardless of the contentType setting.