I recently replaced the catalytic converters and front 02 sensors which caused check engine light to go out. After a few hundred miles, light came back on with the 40 and 45 codes.

What do you think the problem is?

update 9/7/08

The extraction method to get the codes was the round device that is attached under the hood and has a hand held scanner/reader that displays service codes. I don't know the name of the device.