The 2.1.x Hudson build is broken in printing by mapfish print-lib-1.2-SNAPSHOT.jar which has been built with Java 6. Please either remove the -Pprinting from the build or change the dependency to a Java 5 version.
From the test error:
Caused by: java.lang.IllegalArgumentException: Error loading class [org.mapfish.print.servlet.MapPrinterServlet]: problem with class file or dependent class.
Caused by: java.lang.UnsupportedClassVersionError: Bad version number in .class file
I checked the major version in the class file and it is 50 (Java 6).