That fixed the issue. Thanks.

I fail to see how this should solve my problem: I already have a bunch of simpleviewer galleries created by the default Lightroom plugin. Now I need to convert them to juicebox galleries. How can using a newer version of the simpleviewer plugin for Lightroom solve that problem?

Many config options from the pro version are (sadly) not exposed in the Lightroom plugin, but if a static template/preset based on the pro-options is needed, these options can be "hacked" into the Lightroom export by copy/pasting the relevant XML attributes from a gallery created by juiceboxbuilder into the confix.xml file found in juicebox.lrwebengine. However, some config options seems to require another version of juicebox.js than the one that comes in the Lightroom plugin. For example having the thumbs to the left in a 4x6 grid.

Question:
Is the juicebox.js file in the Lightroom plugin just purposely limited in functionality, or will different gallery setups imply different juicebox.js files when the galleries are exported from juiceboxbuilder?

In Lightroom 4.2, create a simpleviewer gallery using the build-in simpleviewer plugin. This is how, I have created numerous galleries in the past couple of years.

Next, open juiceboxbuilder-pro.app (on mac), and open the newly created gallery. Notice, that no images are discovered. Some of the config options are apparently read, but the images themselves are not.