Trouble code P0500 indicates a Vehicle Speed Sensor system fault. Your Toyota Camry has vehicle speed sensors on each of the four wheels installed in order to send wheel speed data to the ABS system (as well as the emission control computer ECC). While your Toyota Camry is being driven on the dynamometer (when only the front wheels are spinning) the ECC sets a vehicle speed sensor P0500 trouble code.
The proper test procedure for your Toyota Camry should be to configure the smog check machine to "Non-Disengagable Traction Control" and perform a "2-Speed Idle test" instead of the loaded ASM test (dyno). We recommend calling a second smog station to see if they will perform a 2 speed idle test. If other stations refuses to test in this manner, contact the State Smog Check Referee's Office for a smog check appointment with them.