Exhaust System Problem with Catless Downpipe

I just installed a RV6 catless downpipe and as expected I got a CEL. I already have the car tuned with Ktuner and was just wondering which code I need to clear to get rid of this message. Thanks.

Catalyst Efficiency P0420 under Main Paramaters->Disables/Monitors

Exactly what I was looking for, thank you.

One more question, the guys at the exhaust shop suggested installing free flowing mufflers such as Vibrant, to fully take advantage of the catless downpipe. I don't see anyone on this forum running those, is there any merit to this claim?

I don't really think the rest of the exhaust is restrictive. The cat is the most restrictive part but since you are catless you are good there. You most likely won't see any gains with different mufflers, resonator, larger piping, etc. Maybe on a higher displacement motor but not with the L15.