2003 Camry with 79,000 miles and I am having my first problem...if you don't count hitting that deer. :)

The engine light came on, went to Discount Auto and they hooked that code checker up which found the following: P0031, H02s Bank 1 Sensor 1, Heater Circuit Low. So I replaced the upstream 02 sensor and cleared the codes by disconnecting the battery and the light came back on after a few minutes. Then the guy at Discount cleared the codes using their computer...the same error came up after a few more minutes. So my guess is that the problem is somewhere else in the circuit...any ideas?

thanks!