It is assumed you are using the jQuery Form Plugin.
If you check https://github.com/malsup/form/ you will find that it mentions that this plugin is dependent on XHR 2 for modern browsers (in case of IE it is only possible in IE10+) and for older versions it uses iframes (http://malsup.com/jquery/form/#file-upload).
It is suggested that you check the above link on the iframe part as it involves a bit of understanding of how the server can access the file.
Let us know if it worked and what version of IE you were testing.