Hello,
According to the Porsche Owner's Manual "if the vehicle is not started or unlocked with the remote control within 5 days, the remote control standby function is switched off (to prevent discharging of the car battery)." To fix: unlock the driver's door with the key at the door lock. Leave the door closed in order to prevent the alarm system from being triggered. Press the center locking button on the remote control. The remote should be reactivated again. I hope it's as simple a fix as that....good luck.