I can' t find how to downgrade Silverlight to a lower version. It seems only version 5 (the one I already had) is available for download.
So I tried setting UploadType="Flash" explicitly on the CuteWebUI:Uploader, to bypass Silverlight alltogether, but then I run into an error in the Ajax Uploader component:
"Line: 1 Error: Unable to get value of the property 'length': object is null or undefined"
I get this same error in IE (without the Silverlight plugin being installed) on your demo page at http://ajaxuploader.com/Demo/select-multiple-files-upload.aspx
The upload itself succeeds, but the error is annoying.