I have no problem accessing other files uploaded via http but this m4a file can only be accessed ftp, when trying to access http I get page not found
A bit more information would be nice. What sort of setup are you running, Windows or Linux? I would make sure the file is actually in the path, if you upload other types of files to the directory your ftp user is uploading to can you access it from the webserver? In the case of Linux the web server runs as a different user and you need to make sure the user can actually access the chain of directories to your file including your file. You get a Permission denied when this is the case though so my assumption without anymore information is that your ftp dump directory is not in an area your webserver can get to.