Upgrade StorageCan't enter book section and book from web tool
There has always been the problem that it wasn't possible to cut and paste an entry. So, if you have an anthology, and want to enter each chapter as a separate entry, you have to enter each chapter individually. The problem was partially solved when I could go to Worldcat and download multiple copies of the book, and then change each one into a book section. Now, things are much worse: I can't enter multiple copies of a book anymore and, once I've downloaded one copy and converted it, any further attempt to download the book entry just fails. You can only download a book entry one single time.
What you were doing before isn't the right way to do this. To create multiple items, just right-click on the item in Zotero and click Duplicate Item.
(You can also just reload the page to save again, but that's not necessary.)