This very very strange.
Please again install manual Joomla Book library
from our site(without remove old version).
Please check: The install process was completed successfully?!
If this not help:
Could you give to us
full FTP and supper admin access
and our team will find solution special for You, FTP and admin access You can send to our contact form.
Link to website.
Detail description: How reproduce error. Step by step. Detail description: how we may reproduce this.
Site Super Admin:
P.S. Please do site backup 2 times per month, it will save you a lot of problems in the future.