This modification to the osCommerce upload class prevents oblivious users from uploading files with names containing characters that are prohibited by certain operating systems but not others (i.e. /:"*?<>|) or that will cause problems with files not displaying correctly in a web browser or with PHP (i.e. %$#). The fix is very simple, either replace your current version of upload.php with the included file or follow the instructions in the text file to manually fix it yourself.
Note: The error message given by this contribution is English only. Someone else will have to modify this to warn the user in any other language.