SVGGenerator.generate() throws RuntimeException on Customer Linux box

We got a customer call today that our app is throwing a RuntimeException (see below) whenever they try to generate SVG for the charts we display. The customer’s web server is on a Linux box (RH ES). But this exception is not thrown in our RH ES-based test environment. I don’t yet know what kind of chart the customer was trying to generate SVG for (in case that makes a difference). I will post that information once I have it. Our app shipped with Vaadin 7.1.15 and Vaadin Charts 1.1.6. The phantomjs version is 1.9.2.

Here’s the exception - hopefully someone has more of a clue than I:

27 Nov 2014 15:36:13:443 | java.lang.RuntimeException: java.lang.RuntimeException: SVG generation failed: ReferenceError: Can't find variable: formatJsJson
27 Nov 2014 15:36:13:485 |  at com.vaadin.addon.charts.util.SVGGenerator.generate(SVGGenerator.java:227)
27 Nov 2014 15:36:13:485 |  at com.vaadin.addon.charts.util.SVGGenerator.generate(SVGGenerator.java:181)
27 Nov 2014 15:36:13:485 |  at com.blackstratus.reports.dialogs.ExportWindow.getReport(ExportWindow.java:102)
...

Thanks for all help/info on what to try.
Tom