I just recently also had this issue. It's not a permissions issue; I was using a download source (legal, don't worry) outside of iTunes. When I went to edit the song stuff, i got the same greyed out info popup, and it wouldn't let me edit straight from the song selection. However, when i re-downloaded, it worked just fine. Same place downloaded from, same destination folder, same everything, but this time, it worked. I then tried to delete the old files from itunes, but it wouldn't let me, so i deleted them from the folders they were in in on my harddrive. Itunes still won't let me delete the pointers in the itunes player, and has the little ! mark next to them now. Also, when added to a playlist, the song cannot be removed from said playlist.
EDIT: It now lets me delete them, after having restarted after deleting the files. I missed one of them though in their XP directory, and that one still won't be deleted in itunes.
Message was edited by: tlaz