If you can mount the player with read access cd to the directory and check permissions. Like this:
$cd /mnt
$ls -l
you should see something like:
drwxr-xr-x 2 root root 4096 Nov 15 19:54 cdrom
drwxr-xr-x 2 root root 4096 Dec 3 07:53 dosc
dr-x------ 1 root root 8192 Dec 10 17:44 windows
the d is for directory and the rest of the letters are for (r)ead (w)rite and e(x)ecute
so if you have:
dr--r--r-- 2 root root 4096 Nov 15 19:54 mp3player
issue:
$su (if your user is not the owner of the file system)
password:
#chmod -R a+wrx mp3palyer/ #note this should be whatever the dir is really called
this will allow (a)ll users read write and execute permissions for that dir (-R)ecursively (meaning all directories including and below /mnt/mp3player