The source version of the EVE-Central uploader available from the main page has some issues working correctly on a Macintosh or Linux system do to bad path separators. Below is a link to grab a version of the uploader from the Git repository which contains a small patch to work around the issues. You’ll need an install of Python and wxPython (Unicode) appropriate for your system in order to use it.
Further up the Git tree is an unfinished UI refactoring effort (that is over a year old). If someone wants to take up the task of trying to complete the multiple-client uploader refactoring, they are more than welcome to.