alonsorobles ,

It's a limitation of the HTML5 <input> now.

The XSD mimetype is application/xml , and the browser will handle it as "*.xml"

So , for HTML5 upload mode , it's not able to select XSD if you want to hide other file types.

Here's two options :

1 - add this script to let HTML5 mode allow select any files :

<script> 

function CuteWebUI_AjaxUploader_OnInitialize()
{
      this.internalobject.SetDialogAccept("*");//which mean HTML5 <input type='file' accept='*' />
}

</script>

2 - force the UploadType to Flash or Silverlight to avoid the HTML5 mode

Regards,
Terry