Technical Support wrote:
First, Will the E640 fire if you press the LED on top of the MC2? If so, then the problem is not likely to be MC2 to E640 related. Does the flash unit fire if its own test button is used (try with and without the MC2 installed)?
Other than a channel/zone reset, I dont know what would cause that. As with pretty much all MC2 related concerns, I will need to defer you to PocketWizard for the most qualified assistance.
LPA (PocketWizard) can be reached at:
802-658-0038 x572
Try reflashing the firmware, and do the tests I describe above. Pocket Wizard will need to be the contact point for issues arising from the MC2 issues, as they manufactured the device, specified the firmware, as well as have knowlege with how they should react to the transmitters, which we are not intimately familiar with .