I didn't experience this myself until I used the Wizards to upgrade the Age. Then found out that the Wizard is for pre 1.0.0 Ages (because I didn't bother reading the tutorial, so MY fault on that one

)
However, I went through and removed all the col_flags, deleted the book and created a new book, etc, etc. I've been over the Age with a fine tooth comb and come up empty handed.
I have this happen if I just change something in the python files too!
Now all the other Ages: Zephyr, Andy_Nexus, Dot's Office, Camp Bravo Day Time, they all load just fine with no problems. But I haven't tried to make any changes with them......yet.
Of course due to the large amount of changes in the plugin, it's not as easy as just "roll back" to an earlier plugin to see if that's the problem as I'd have to go in and change everything again. That's a bit much to do, hehe.