its the immobilizer ring attached to the key socket under the rubber shield that is causing your problem. when it gets wet the ring doesn't register properly. this is a known issue and one I deal with every now and then.
you can either wait for the system to reset on its own, usually after a few hours of drying out, or you could manually input your immobilizer code. the code is on a tag that came with the spare key. the exact procedure to access the code input screen should be in the owners manual. sorry I can't remember it now.
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