Same thing happened to me when my battery died on my rex. I called road side assist to come out, replace the battery, and then he tried to reset it to no avail. I then had it towed to a Subaru dealer who also couldnt get it working. In the end, they found root of the problem being one of the modules was cactus. Once that was sorted, all was good for then on in.

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Previous Car, MY05 WRX