It looks like the ISBN variable is the culprit. We do a call to Amazon to create a link to the book automatically, and somehow that call is no longer working properly. I've fixed the issue in the code, but unfortunately we will have to wait until our next release (in 7-10 days) before the problem will be completely fixed on the live site. I'll see if it's possible to expedite the process, but it may not be feasible at this point.
For the record, if you remove the ISBN variable, it will make the waymarks work again, but will lose all the ISBN data for all the other waymarks in this category, so I don't recommend doing that.
Sorry for the frustration,
Bootron
Thanks!