Auto Delta Compensation crashes into Z Tower

Please can anyone help a newcomer?...

I've just built my Fisher and am running through commissioning. I have gone through all the steps up until Bed Probing successfully.
I can move the head in each direction and the correct distances using the web interface.
But, each time I try and execute Auto Delta Compensation, the head crashes into the Z Tower (to the left of the Duet Ethernet/ Power sockets).
The steppers keep driving until I can get to the Emergency Stop - by which time some of the rods have disconnected.

Can anyone point me in the right direction?

Thanks

If you have deployprobe.g and retractprobe.g files in /sys on the SD card, delete them.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Excellent - many thanks.
Odd that those files are on the SD card that ships with a Fisher and there isn't a note to delete them in the build instructions.