Twice in the past few weeks I tried to upload two different files using the Upload a new version of this file link and both times got upload warning errors about not being able to rename the file.
You probably don't have the rights to rename a file.
Try uploading the file with a slightly different name. If that works, edit any references to the original file so that they link to the new file. Then, send me a PM so I can delete the original file.