Hi,
Looks like the DNN 5 upgrade doesn't quite get the HttpModules/Handlers right in the web.config.
I setup a DNN 5.2.3 test website and then installed DMX 5.2.2 in it and it worked fine !
Then I examined the working web.config with the failing one and copied over exactly the bring2mind entries
and the RadUpload error went away.
LA Guy ( Paul )