someone please tell me how to fix this!!!!!

[TheSentch]

i have a stillen header and mid pipe on my 02 spec v there for there is no first cat. well i used the simulator box that stillen sent with it and that didnt work. then i got another simulator and that didnt work. so i ran the codes again and this is what it said P0138 O2 Sensor Circuit High Voltage (Bank 1 Sensor 2) and i cant find anything that will tell me exactly what it is and how to fix it