Max file upload size first needs to be set using the modeler.. There is also a setting on webservers which defines the max file size, you should contact Mendix (support ticket) to change the property (i think it's called client_max_body_size?)
This setting is set to 1GB on web servers, so effectively letting the runtime handle the limitation instead of the intermediate web server. It might be different if you are using an old putty cloud environment.
Can you clarify what "an error" and "no joy" means?