Thread:Extension talk:Collection/Creating a book with multiple pages fails

After much effort I got the Collection extension to work great on my wiki for PDF'ing single articles. Unfortunately it still is not working for multiple pages, and I haven't spotted anyone else having the same issue. Using "Create a Book" with 1 page renders perfectly, but the moment I have more than one article in the book it fails with this error:

Here is the command I'm using for my local PDF generation service (using supervisord):

[program:nserve] command=nserve [program:qserve] command=mw-qserve [program:nslave] command=nslave --cachedir /data/mwcache [program:postman] command=postman --cachedir /data/mwcache

And the relevant section of my LocalSettings.php:

require_once "$IP/extensions/Collection/Collection.php"; $wgCollectionMWServeURL = 'http://127.0.0.1:8899';

Again, this configuration works great for single-article PDFs; only multi-article PDFs are failing. Any help would be appreciated!