It turns out that VCS and Questa have different opinions about what constitutes an error when using pure virtual classes.
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Questa says that it is OK to write code that could instantiate a pure virtual class as long as no pure virtual class is ever instantiated.
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VCS says that it is not OK to write code that could instantiate a pure virtual class.
Several examples (starting in chapter 13) use a pure virtual class to define a base_tester class, but then override that class using the factory. VCS does not like these examples.
To fix this I've included a file named vcs_base_tester.svh. To use the vcs_base_tester.svh file simply copy it over the base_tester.svh file in directories where you see it.