Simple Z touch off generating empty error [SOLVED]

I'm adding a touch probe to a ChinaZone 6040 with a Mesa 7i76e card following what seems to be pretty simple instructions from forum.linuxcnc.org/49-basic-configuratio...obe-with-a-mesa-7i96.  It's really close, but generating an error. 

When I click on "Tool Touch Off Z" in the side panel, I get a blank error (see attached pic):
<l> (?) [x]

Where should I look to find the problem?  I've gone through the example a few times and am just missing it somehow.  I've checked the Linux logs, but haven't found anything yet.

• Axis 2.8.4 (I can upgrade if that would help)
• Hal Meter signal probe-in turns to true when the touch probe is triggered, so the wiring & HAL seem correct
• I've run each of the commands in the ngc file using the MDI tab and they all function as expected
• The 5 updated files are attached and each has it's full path in the comments at the top of the file
  
  Thanks,
  Ted

D'oh!  Figured it out.  In case anyone else is as slow as I am...

In the ini file, my comm "MDI_COMMAND=0 <z_touch> CALL" was the 15th item in the HALUI list (starting with 0).  So my custom_postgui.hal file should have been:
net ztouch halui.mdi-command-15 <= pyvcp.ztouch

All good now.  Just need to measure offsets and we're running!