I have a Bryant 373LAV Horizontal Gas Furnace and am receiving effor code 12 which states "Blower on after power up (115 or 24V)" what does this mean. How can I fix it? HELP!!

This code should only appear when the unit is powered up with a thermostat call for heat, and only last for the selected blower off-delay period, followed by a heating cycle. Re-check to see if any other codes are displayed and post back (allow time for blower off-delay to time out-usually 1 1/2-2 1/2 minutes).

I have tried letting it run for an extended period and this is the only error code I get. I have reset the power a couple times in addition.

Does this same condition occur with the thermostat set to "off"?

I hate to say it but this is sounding like a faulty circuit board. Look closely for evidence of moisture exposure and/or oxide bridging of the circuit paths on the board. Something has likely shorted the timing circuit.