It's a small leak somewhere in your canister purge system. Not a big leak like leaving the fuel cap off. Check to make sure the service port cap is secure on your canister purge valve. The valve is on the firewall behind the motor, and the cap is green.
Failing that, has there been any recent service to your fuel tank, fuel system, or motor in general that might have resulted in loose connections?
A CEL means the leak was detected on two consecutive drives, so it wasn't a one-time shot.
What happens is the system is sealed off and manifold vacuum is used to pull a vacuum on the vapor lines and tank. Then the PCM monitors the bleed-up pressure rate and either concludes the system is good, has a small leak, or has a large leak.
Really vaporous gas can cause a false leak code, too, since it increases the pressure in the tank, making the computer think there is a leak. So if you've recently tried a different brand of gas, that may also be causing this.
If there is nothing obvious in terms of connections, reset the computer, let the car sit for six hours minimum, then drive steady on a highway at about 60 for about 10 minutes. The car can't be too full or empty on gas to run this test. Somewhere between 1/4 and 3/4 tank is good. And avoid sudden throttle changes or lane shifts. Repeat this same cycle on the next power up, after letting the car sit for at least another six hours. If you have some interstate on your daily drive, you are probably running this test going into work and coming home on the same day. Just don't go out at lunch.
