cutechat: Hi, I am not sure what's wrong now. because I can't reproduce it on your website. please add this into web.config and try again. <add key="CuteWebUI.AjaxUploader.UseAspNetStream" value="True" /> and also , you can let the user test this page https://portal.denora.com/TEST/TestUpload.aspx?UploaderDebug=1 it will show a debug trace box , when get error , please copy the text and paste here . Regards,Terry Hi Terry, thanks a lot for your kind answer. We have just modified the web.config on our two WebServers, adding the UseAspNetStream key. Our user will test the upload again and we will let you know the result. If the error will still show up, the user will make another test using the debug mode on the TestUpload.aspx page, as you suggested. Best Regards, Tux.