I got similar problems, but this was not solely with Zortam.
Sometimes there are files I can play but cannot change anything (even the tags). Those cannot be changed by another tag editor neither. I had to resample them with some prog.
Then I had a file with a special character somewhere in the tag (spanish question mark: ¿). There I couldn’t normalize but could change the tag. I removed the special character and it could be normalized. And after this I could add the special character again.