Editing Song/Album Info Not Working

I've purchased several albums from non itunes stores. With several of these albums I have been unable to edit the information of the songs (genre/equalizer, etc). What happens is, I will open the file on itunes, write in the changes and press enter and none of the changes will stick.

Occasionally I can change the info on individual songs, but even then sometimes the song info will revert back to the original info.

After using itunes for close to 20 years, this is the first time I've had this problem.

Any solutions???

Thanks!