10tklz relocated the Library to the SD card, not individual books, using the following procedure:
https://www.entourageedge.com/suppor...barticleid=134. Opening books from an SD card, like you're doing, isn't a problem. Seems 10tklz is having issues with books that were added to the Library later "disappearing" I think.
I just checked, though, and that procedure gives you the option of "Internal Storage" and "SD Card" for the Library, so in theory 10tklz should be able to switch it back to the internal memory, given that the Library will still fit in the more limited 2-3 GB of space.