G code question when running autolevel

I am running LinuxCNC 2.8.2.11 and Autolevel 0.8.7
I get a error when I load a autolevel file

Near line 281 of..........AL6X6.ngc
Unknown word unary operation could be

N11 Z0.118
#102=#500
#101=#500
#100=[#102+NaN*#101-NaN*#102]
N12 G1Z[#100 + -0.1] F3.937  (this is Line 281)
#102=#500
#101=[#500+0*#507-0*#500]
#100=[#102+0*#101-0*#102]
N16 X0Y0 Z[#100 + -0.1]
#102=[#500+0*#507-0*#500]
#101=[#501+0*#508-0*#501]
#100=[#102+0.187*#101-0.187*#102]
N13 X0.187Y0 Z[#100 + -0.1] F20

I do not understand what the line is trying to tell me or how to change it.
Any help would be welcome

Jan

This Line is highly suspicious, containing unknown gcode



#100=[#102+NaN*#101-NaN*#102]

Thanks for the comment
-0.1 is the Z depth of the cut in the program. I assume the line means #100 plus -0.1. but I am maybe just guessing
Jan

Thanks for the reply
I have no idea what NaN even means but it only shows up once in 816 line program.
Jan

Thanks
You could be right. I don't know why this line came up but it doesn't when I load other autolevel files. Must be a quirk in this file. I did delete the line and the program seemed to run fine.
Thanks again
Jan