My report and form were built using the Apex tool wizards. By process of elimination I realized that the error was coming from the 'display only' field I had put on the form for one of the file uploads that I did not want a user to change. So I rebuilt the form/report so the interactive report just shows the viewable downloads (uploaded previously) by other users and the Form only shows the appropriate field for uploading new files. I get no more errors.
Thanks all for replies!