If you are having difficulty with a file or a file has become corrupted, sometimes we will suggest doing a Layer Import to salvage data from the original file. In the event that you can't open your original file, often doing a Layer Import can still recover data from that file.
Information about doing a Layer Import can be found here.
Doing a Layer Import can also be a useful way to copy objects from one file to another while maintain the object's Class AND Layer information. (Simply copying & pasting objects from one document to another will just place the object on the active layer in the new document.)