One key works the other does not

[PowerMalc]

The key I have been using since I got the car 2 years ago has virtually stopped working in unlocking the car
The other(spare) works fine. So I swapped the batteries and its still the key Both keys flash red when you press the buttons.
I tried the manual suggestion of holding the key on the side of the windscreen as you press the buttons, this worked a couple of times but now nothing.
Anybody got any ideas please

Car is a Boxster 981 Sept 2013

[Pope]

Could just be a case of resynchronising the keys; in turn insert the keys in to the ignition and switch the ignition on; within five seconds press the unlock button on the key - if the resync works the dash led will flash.

Working keys can be re taught if you are still having problems

[ellroy]

Funnily enough I have the same issue, also 981.

The OPC told me to bring it in to have it reset when I'm next in.