UPDATE: CoPilot finally solved my problem by resetting my Google Checkout number on their system, might be worth asking them to do that if you’re having the same problems!
Seeing as there doesn’t seem to be much relating to this error on Google. Well, there does, but never a resolution (or people are unwilling to share the solution they received from CoPilot).
I had the notorious “Google Checkout number invalid” error, and after re-installing the app, then received this error when trying to log in to my CoPilot account (on the phone): Sorry! Your CoPilot Trial Has Expired – Error 703
So, for the benefit of those of you out there who encounter this problem, here’s the email I received from CoPilot regarding this problem.