(BTW, I tried your "Quick Reply" option, and other than it appearing in a too-small window, as I was almost done my reply, the control completely erased, and I lost all my text!)
Thanks for the suggestion for trying the link. It was successful, and I tried the UploaderDebug=1 option, and compared the output.
Yours:
INFO silverlight report,response,1c14e6d7-34a5-49ae-88b2-2fa207a980a5,OK,
Ours:
ERROR silverlight report,error,02f0d634-3e1c-4e37-90ce-5e81ce512a6c,io,WebException : UnknownError,[HttpWebRequest_WebException_RemoteServer]
Arguments: NotFound
Debugging resource strings are unavailable. Often the key and arguments provide sufficient information to diagnose the problem. See http://go.microsoft.com/fwlink/?linkid=106663&Version=4.0.60310.0&File=System.Windows.dll&Key=HttpWebRequest_WebException_RemoteServer
We uninstalled AVG Anti-virus on our host computer, then tried it again, and it works.
Unfortunately, this computer cannot do without a working anti-virus solution, so we are looking at this as a "limited win" until we are able to cover our assets and upload at the same time.
Thank you for your help. Please consider adding a section in to your FAQ regarding the Uploader about troubleshooting aggressive anti-virus solutions.