Cannot connect ICE-2000 to custom board with ADSP-SC572

We have a custom board with an ADSP-SC572. We've checked what seems to be everything: power rail ramps, reset, clock, and everything seems fine. The ICE-2000 looks like it wants to connect but then we get a FAULT LED on the board and this message in the tool: Error: Failed to connect to target., Code=0x80047344

We know the ICE-2000 works, so it's not the tool. (checked it with a demo board). We have a full license, so it's not a problem where the ICE-2000 is crippled where the ICE-1000 isn't. (And the ICE-1000 we have shows the same behavior as the ICE-2000)

JTAG testing seems fine.

We have a source oscillator of 24MHz feeding CLKIN0, and we do see SYS_CLKOUT doing the right thing.

Has anyone else had trouble connecting to the ARM of an ADSP-SC57x?