So I tried it again. Same result. Again. Same.
This is odd, it worked just the other day, and I don't think any changes have been made. So, just for kicks, I tried selecting a handful of books and renewing them individually.
Interestingly, it went through. It seems, however, that the renew script chokes when you try to renew 19 books at one time.
Oh, yeah, now my team leader is making fun of me for it, and calling me the "South Wing Library". I want to tell him to bite me, but he's mostly right.