The data you're posting is not valid JSON. Decoding the string reveals:
ar[0][]=8594&ar[0][]=K02R019&ar[0][]=K02&ar[0][]=IB-K-29&ar[0][]=TRACKWAY&...
That's the standard
application/x-www-form-urlencoded
format used to submit a form.
Change your AJAX call to:
$.ajax({
async: true,
contentType: 'application/json; charset=utf-8',
dataType: 'json',
type: "POST",
data: JSON.stringify(arrays),
url: "myHandler.ashx",
success: function (result) { }
});
You should then get a valid JSON string in your
stream
variable.