Add the following error event to your Ajax call
success: function(data) {
lat = data.results[0].geometry.location.lat;
},
error: function(xhr, status, error) {
alert(status);
}
And let us know what error message you get in IE, if any at all.
EDIT - Sounds like you are trying to do a cross-domain request?
If that is the case, try setting $.support.cors = true;
before your ajax request.
Fetched from http://api.jquery.com/jQuery.support/
To enable cross-domain requests in environments that do not support cors yet but
do allow cross-domain XHR requests (windows gadget, etc), set
$.support.cors = true;
EDIT2 - Ill assume you are running IE9, in that case you need a plugin for jQuery found here:
https://github.com/jaubourg/ajaxHooks/blob/master/src/xdr.js
Also see this answer on SO for more details on why a plugin is needed for IE9 (with cors): IE9 jQuery AJAX with CORS returns "Access is denied"
EDIT3 - Download jQuery.XDomainRequest.js and include it before your AJAX call.