It was working fine for quite a while then it wouldn't boot so I reinstalled using the 16GB Class 4 microSD card.
It ran for a while and failed again so I ordered a Sandisk 16GB Class 10 microSD, installed Ubuntu again but it fails to boot or output to the serial console which is registered as ttyUSB2.
I purchased it from Farnell UK but their site doesn't suggest a way to do a RMA.
How to do a RMA for it?
Why don’t you try the original bone SD card to test the issue?
As part of the RMA process, you’ll need to try the original SD card image. See the SRM and website for RMA details.
OK I'll do that if that's a pre-req.
When it fails what do I do?
Go here: http://circuitco.com/support/index.php?title=Main_Page
Follow the link that matches your board. Instructions will be there on how to recreate and SD card if you need to.
Then you will need to go though the RMA process if it still does not work go here:
You will also find instruction in the System Reference Manual on tte RMA process.