Interesting. I've had cars sit for over a year and fired right up once a battery is installed.
Maybe the ignition immobilizer antena somehow got damaged?
The immobilizer system consists of key chip, speedo cluster, BIU, ECU, if any of these are changed, it does exactly as your car is doing.
The key is read by the BIU, I'm pretty sure. I have reprogrammed immobilizer on many subaru's.
Again, I'd guess maybe ignition antenna.
Its the white ring around the ignition where the key goes in.
Also check all fuses.