drutil eject
I'm going to assume this isn't the issue since, if he tried both of my original ideas, he would have restarted his machine. Good thinking though.Were you using a windows emulator (Parallels or Fusion for example) when you inserted the disk. I've been caught out by this several times. If you are in Windows when you insert the disk it won't eject from the mac and visa versa.
for i in $(mount | grep read-only | awk '{print $3}')
do
j=$(lsof | grep $i | awk '{print $2}')
kill -9 $j
drutil eject
done