Hmmm. You haven't been adding or removing files from an "esi-content" folder on the SD Card I hope... I'm assuming that if the Library is moved to the SD Card it will still be in a folder called "esi-content". I mention this because if you add/remove files directly, the Library app won't be aware of it and when you try to open a file using the Library app, it won't be able to find the file.