When an upload with the Commons Upload Wizard fails it should display an error message about what exactly went wrong such as "a file with this title already exists". As of right now it only displays "None of the uploads were successful." with a button to "Retry failed uploads" which is useless for actually correcting the error.
Furthermore if a file with that same name already exists it should display link to said image and preferably its thumbnail so users can check whether it's the same image.