User2103319870 posted
Did you register the RadUploadProgressHandler in web.config?"
But I already register the RadUploadProgressHandler.aspx in web.config.
If you manually registered RadUploadProgressHandler.aspx , then try registering the RadUpload control using the SmartTag. You can
refer this article.
However your should consider replacing your RadUpload control with RadAsyncUpload as RadUpload control has been discontinued from June
2013 (Q2’13) as per their documentation.
I used RadAsyncUpload control and it worked fine with out registering any handler .
Hope this helps.