No I'm not blaming the brand of mod either, its been found before that aftermarket dumps can play with the smart ECU/02 sensor relationships. I think there are others out there who have had the CEL with all kinds of dumps (no idea if they had the same code as you)
Agree with gumbyy above - The way the explanation reads for your error code - it points more towards the sensor being able to detect the cat not working within spec of the expected values in the ECU.
Probably doing no harm to performance but perhaps emmisions??