Class version 51.0 means the class was compiled by a JDK7 javac and you are trying to run it on a pre-Java 7 JRE.
Use the -source and -target switches to javac and instruct the compiler what language level you require (e.g. 1.5):
javac -source 1.5 -target 1.5 src/com/chrisnewland/test/
If you are using ant, add these as attributes source="1.5" target="1.5" to the javac task.