Animating a Book in Blender

I´m following a youtube tutorial for creating a book and animating the pages and the covers.

https://www.youtube.com/watch?v=yQGLdW0ioss&t=439s

Until this part, I´ve been able to follow it, but now, I have a problem in part 4 minute 7 that I can´t solve.

When I duplicate the thickness bone, ´Pages.R´ breaks and creates an random form.

Someone who is familiar with this tutorial could lend me a hand?

Also if you need help with something of the videos 1, 2 or 3 I´ll be glad to help if I can.

Thanks!!