Messages

On the 60D, I found the cause of my error.  I was shooting Raw-Small for testing purposes.   ETTR works fine in Raw (large) mode.

In the raw-small and raw-medium capture modes, "press set" produces no error message.    Whatever the problem slamming is still having seems the same as the other raw size capture modes.   Maybe you could debug the 6D using the 60D small-raw feature.

I too am getting the "Raw error" message slamming is getting.

Camera 60D, Nightly Build Mar29, fresh SD install.

Only occurs when Auto ETTR is on and set to Trigger modes: "Always ON" or "Auto Snap"
No error when Trigger Mode: "Press SET"
Shooting RAW only

Occurs with Overlay Histogram Off or On and intervalometer Off or On.  Problem occurring from the very first attempt.