Both times it happened, the router was raising the Z axis for a tool change.
First time was in the middle of a tool change subroutine after the tool had been loaded and seated properly. Z-raise, then ATC arm actuated, tool seated and locked, then Z raise, retract ATC arm, then E-stop.
Exiting TWD software and restarting yielded the same result on the same code, I tried that twice.
Complete shut-down, power off, then reboot and the same code ran fine.
Just happened again, at the beginning of a tool change subroutine, on the initial Z-raise prior to the arm actuating (is that a word
) to receive the tool. 
I've just shut down for the day after the second incident.
Any ideas?
Perhaps a corrupted tool change subroutine?
