Is the schematic for the FW PIC18 main board correct (FW Main-R2 Blue dated 14/02/14)?
I just noticed that it shows VUSB for the 18F14K50 (pin 17) connected to Vsupply. That would be a real problem, esp. if the board is jumpered for 5V operation. Since it's the output of the internal 3V3 LDO regulator it should have a capacitor on it, and that's usually it.
I tried metering it out and couldn't find anything connected to pin 17 that I noticed. Is there any connection to pin 17?