Eugene, I'd be guessing but it sounds like it's be bank 2 and post cat sensor...
But, 02 sensor codes often seem to come about because of other things pretty often...though with only one 02 code (assuming the heater is built into sensor) that might be more reliable.
I do know that cats on an older 750 have heaters independent of the sensor, but don't recall that on an e36.
I'm so depressed. No one wants to come see me. :(
Mangofy your E46!