Error when validating Xtext DSL in standalone Java project

I recently followed Sebastian Zarnekow's short guide on how to deploy an Xtext DSL into a standalone project (found here: http://zarnekow.blogspot.co.uk/2010/06/how-to-deploy-xtext-standalone.html)

However I receive the following error when attempting to run the project...

"The string resource '_UI_DiagnosticRoot_diagnostic' could not be located"

Could this be something to do with how the JAR is exported, I chose the "Extract required libraries into generated JAR" option, if I try to use the second option where the libraries are packaged into the JAR I receive a different error telling me that a main method could not be found.

Has anyone come across this issue before? I tried updating EMF and Xtext but it didn't seem to have any affect.

Any help is appreciated.