I have an SBC account also. As cantaffordit suggests above, don't use the Yahoo settings as the SBC account won't be recognized. The standard (generic) account worked to get mine up and running.
I had the same issue, but I went into my touchPad settings and found my clock was off by 10min with network time on. I turned it off and reset the time. Yahoo Mail then worked.
I had the same experience as zigzag6 using 2 Verizon/Yahoo accounts, resolved by turning off internet time in the "Date & Time" settings, and updating the tablet to the correct time.