Can't add new section or chapter in iBooks Author

(Let me state at the outset that I am an iBooks Author newbie....)

I changed to a new laptop and so re-installed iBooks Author from App Store. I open a template from within iBooks Author, and then set about customizing it to my needs. But I cannot get it to add a new section (a Forward, for example), chapter--not anything. I have even tried going to the Insert menu and adding a new Page (chapter or section) this way, but all that happens is I get a progress bar that says "Updating Pages". This bar would literally run for an hour, with no change in progress, even all night, if I let it. Eventually I just force quit.

Any ideas what's going on? I tried trashing iBooks Author app and re-installing a new one, but I get the same problem.