Just heard from Crucial and they accept the results of the RAM tests and will replace the faulty chip under their lifetime warranty, they have even provided a 'freepost' mail label - great service from Crucial!
They want me to run more tests to determin which is the faulty chip (I have 4 x 4GB), do you have any idea how to do that via software or is it a case of taking each chip out and keep running the test again until I find a configuration that returns no errors?