·I get a 'hardware revision check failed' message when I try to upgrade!
Chances are, you downloaded the wrong upgrade file. For instance, you have a Mark 2 or a Rio Car unit, but you downloaded the "car1" version of the upgrade file.
Make sure you get the correct file for the unit. If you have a Mark1, it has "car1" in the file name. If you have a Mark 2 or a Rio Car, it has "car2" in the file name.