uploading using ajax and uploading class

[eluser]phazei[/eluser]
I created a form that is submitted through ajax. When I submit I get the error "You did not select a file to upload."

The form field names are correct. If I change it to a normal submit button, it works just fine. But when I use ajax something goes wrong.

If I do a print_r on $_POST and $_FILES the $_POST has the file name listed with the correct array key, but the $_FILES array is empty.

I'm not certain if CI allows use of the $_FILES array, but I'm guessing it does. Since the post has the name, something is going through. What could be the problem?
Assuming the $_FILES array is working, I'm inclined to believe the problem lays with the ajax, but I'm not sure.

I'm using the correct enctype on the form.

Oh, and I'm doing the ajax through jQuery and the jQuery Form Plugin( http://malsup.com/jquery/form/ ) which seems fairly popular.

Ideas?

Thanks.