If it was in series with a capacitor, connected across an inductor, then the resistor and capacitor are likely a snubber network.
I assume this is part of the PFC pre-regulator circuit?
Wouldn't at all be surprised if not only the diode, but also the associated MOSFET and perhaps even the PFC controller IC are toast. Probably an electrolytic capacitor associated with the PFC controller went bad, causing it to malfunction and switch erratically, overheating the snubber resistor, once that went open the excess ringing from the lack of a snubber cooked the MOSFET and diode. This is a fairly typical cascade type failure I've seen a few times, one bad cap can cause the release of a lot of magic smoke!