sh!t i got that message at 55k, except it was PO430, which is on the opposite side. i've posted about this before in several threads. i couldn't determine that the cat had actually failed so i just let it ride and eventually the CEL turned off. it just turned on a couple weeks ago again with the same error code. hey, as long as i pass smog check i don't care.
one suggestion that was offered was to swap the O2 sensors from the drivers side to the passenger side, wait for the CEL to come on, pull the code and see if the error message follows the sensor OR if it stays on the same side. that way you can determine more easily where the source of the problem is. i never did this but its a good idea.