I haven't seen any '08 TSBs on the keys yet. Did you try to have the system "learn" the key that doesn't work?
Here's the procedure for 2008 models (from the most recent owner's manual):
You can program your own Integrated Keyhead Transmitters or standard
SecuriLock™ coded keys to your vehicle. This procedure will program
both the engine immobilizer keycode and the remote entry transmitter
portion of the IKT to your vehicle. Note: A maximum of eight coded
keys can be programmed to your vehicle; only four of these eight can be
IKTs with remote entry functionality.
Tips:
• Only use Integrated Keyhead Transmitters (IKTs) or standard
SecuriLock™ keys.
• You must have two previously programmed coded keys (keys that
already operate your vehicle's engine) and the new unprogrammed
key(s) readily accessible.
• If two previously programmed coded keys are not available, you must
take your vehicle to your authorized dealer to have the spare key(s)
programmed.
Please read and understand the
entire procedure before you begin.
1. Insert the first previously
programmed coded key into the
ignition.
2. Turn the ignition from the 1 (LOCK) position to the 3 (RUN) position.
Keep the ignition in the 3 (RUN) position for at least three seconds, but
no more than 10 seconds.
3. Turn the ignition to the 1 (LOCK) position and remove the first coded
key from the ignition.
4. Within ten seconds of turning the ignition to the 1 (LOCK) position,
insert the second previously coded key into the ignition.
5. Turn the ignition from the 1 (LOCK) position to the 3 (RUN) position.
Keep the ignition in the 3 (RUN) position for at least three seconds, but
no more than 10 seconds.
6. Turn the ignition to the 1 (LOCK) position and remove the second
previously programmed coded key from the ignition.
7. Within twenty seconds of turning the ignition to the 1 (LOCK)
position and removing the previously programmed coded key, insert the
new unprogrammed key (new key/valet key) into the ignition.
8. Turn the ignition from the 1 (LOCK) position to the 3 (RUN) position.
Keep the ignition in the 3 (RUN) position for at least six seconds.
9. Remove the newly programmed coded key from the ignition.
If the key has been successfully programmed it will start the vehicle's
engine and will operate the remote entry system (if the new key is an
Integrated Keyhead Transmitter). The theft indicator light will illuminate
for three seconds and then go out to indicate successful programming.
If the key was not successfully programmed, it will not start your
vehicle's engine and/or will not operate the remote entry features. The
theft indicator light may flash on and off. Wait 20 seconds and you may
repeat Steps 1 through 8. If failure repeats, bring your vehicle to your
authorized dealer to have the new key(s) programmed.
To program additional new unprogrammed key(s), wait twenty seconds
and then repeat this procedure from Step 1.
HTH...