The tools in the subject line suddenly decide to stop working. I'm shown a Windows message box with "Failed to set emulator mode. Unable to continue." The LEDs on the jtagice behave normally.
I've been through several iterations of unplugging/replugging USB, power cycling everything, restarting AVR Studio, restarting the entire computer, and swearing. Nothing has helped.
This happened a few days ago. Then, I came back the next day, did something silly like restarting AVR Studio (not that I hadn't the day before), and everything started working again.
Just now I have disconnected the jtagice and replaced the 6 pin ISP/PDI cable on the stk600. Still trouble: the stk600 cannot read the atxmega's signature.
I wonder about my powered USB providing enough current to keep both dev tools happy. I'll still post this and look into that possibility tomorrow.