I'm bringing up a new PCB using an ATTiny841. Via Atmel-ICE, I can read the device signature and set fuses (I've set SUT_CKSEL to EXTCRES_8MHZ_XX_1KCK_16CK_16MS for a 16 MHz crystal), but when I try to program my ELF I get the error below. I've dialed the interface speed down to 100 kHz, but still no dice. Any suggestions? Thanks.