• • Error(s) occurred and the instrumentation process can't continue.
    [18:15:19]: [javac] com.cenqua.clover.CloverException: /path/to/my/test/src/some/package/MyTest.java:21:1:expecting EOF, found 'import'

It turns out that one of the import statements had an extra semi-colon, for example:
import java.util.Collections;;
^

I had not noticed this because javac accepted it and the test executed/passed locally without error. However, Clover's instrumentation crashed and failed on the build server.