Are you missing a catalytic convertor? Or is your's on the non-approved aftermarket list?
I believe that it's a requirement to have the stock catalyst it was equipped with from the factory to remain in place for at least 8 years before you can remove it. You must still reinstall one in it's place of course, but California does allow for the modification of exhaust systems as long as the factory-equipped emissions equipment remains in place. Failing you just because an aftermarket system is installed without verification of the catalytic convertor doesn't seem right.
http://www.arb.ca.gov/msprog/aftermk...ftermktcat.htm