Cannot update / correct ID3 tags

For a large number of the songs (maybe 30% of a couple thousand) in my itunes library I cannot change the ID3 tag information. Some it tells me "error the file may be write protected" others I update it but the change never takes effect. It seems to correspond to the songs that were added to my library a long time ago as opposed to the more recent additions. I have repeatedly verified that there is no write protect attribute on the songs but I still can't update the tags. Is there something I can do to fix this? Is there an external tool I can use to force the changes? Some of the ID tags are completely wrong and it causes the entire itunes library not to be organized properly. For example some songs only have a copy of the file name in the ID3 tag and no other data.

I have tried updating and using the most recent version of iTunes and it doesn't help. Thanks.