MTPPC: Sorry to hear about your unfortunate run of luck with the AVRs.
Everything I've seen points toward AVRs being pretty rugged.
Sharpfork posted on another board:
I had the thing completely wired wrong to the point where it got hot enough to discoloer the little piece of masking tape I put on it and it still works fine. Hell, Rodney even boiled one of the AVRs in water based black dye and it still works. These little buggers are tough!
I'd check both your ground and your wire routing/distances. If you have relays, solenoids, shaker motors or AC wiring too close to unshielded wires, the expanding and collapsing magnetic fields can induce a voltage spike.
Your problem may be similar to what Supafraud was posting
here about his mini-pac resetting when he would press flipper buttons.
I haven't even ordered my MinimusAVR yet, but will be thinking about trying to program it using the info linked above, if the new software isn't released by the time I've built my panel.
Degenatrons has some AVR Encoders already programmed (firmware upgrades effortlessly to KADE), labeled and soldered. If you don't have the AVR and terminals yet, and plan on only doing 1 or 2 AVRs, it will probably be less expensive to order from him. (PM him for details.)

Scott