I figured it out.  While it is possible to build without Flex Builder, you need to have the libraries that come with Flex Builder.  The free Flex SDK does not contain all the libraries that are used here.  In particular, I needed these:

datavisualization.swc

qtp.swc

automation.swc

automation_agent.swc

automation_dmv.swc

automation_flashflexkit.swc

and the locale resource bundles associated with these.

The error in question involves a class from the datavisualization library, the others seem to be dependancies of that library. Nothing in any of the code uses the mx.charts stuff, so I can only guess that its something in the corelib.swc or flexlib.swc libraries from SparkWebCommonComponents.  Where did these come from? What license are they under? Is this something we can fix?

Note: The Flex Builder is not free. It is unclear to me what the licensing of these libraries are under, but I presume the same license as Flex Builder. 

So legally I can only use these for the 60 day trial, unless I fork over the $250 for Flex Builder.