Cristina,
Failing the suggestions by Monika, you may consider whether you may have an original set of sound files, maybe on a harddisk that can be attached externally; if the files can be transferred through a USB stick or similar her zipping suggestion may also be crucial.
To me the error messages seem to indicate a corruption of some bit(s) of code, maybe something wrong inserted or something missing, maybe at the very end of the file.
You could try to File>Place the/each ailing document in a new document, maybe with some simple artwork such as just a rectangle, and see; I doubt whether new artwork can make a difference, but I remember a post in an old thread with such a rectangle, and success.
Or you could try to open the file in a text editor and post the last part of it; some friends here can easily spot such wrongness if (luckily) included.
Failing everything else, I believe this case would call for our asking an Adobe staff friend that may be able to (get another friend to) come to your rescue.
Edit: sound files = healthy files, if anyone was puzzled.