The fuel pressure regulator is controlled by the ECM using a PWM output voltage. If the connector or wiring are damaged, mis-connected, or disconnected the regulator will not get the correct signal. I would would check all of the wiring first. There could also be a problem with the fuel pressure sensor, but that generally results in a different code.
The next step in the service manual is to remove the high pressure fuel pump and inspect the camshaft lobes that drive it. If the lobes are worn, replace the camshaft. Otherwise replace the pump.
After checking wiring, the logical thing in my mind is to replace the HPFP.
Sky NA 2007 Midnight Blue
Sky RL 2008 Carbon Flash - Naked