2 things
some file extensions you can't write to a file directly, some will create sidecar files though .. not sure what are the limits of iso files. But I'm pretty sure you can't write to them.
Another thing to check is to see if you have indeed set the flag to write to the files -- for audio flac, alac and with some limitation using wav and mp3 etc most can be written to the files themselves. Check Options=>Library&Folders=>Manage Library Fields ... the "Save tag in file when possible" box should be checked if you want the metadata embedded in the file.
PS - to edit tags from a client (and you are using JRemote as a client) you need to use Authentication with an access key. If you have set up JRemote for direct IP connection, its going to be read only.
