THC Control Issues

When I run the THC Control test with the grounding clamp on the slats I get error and low live voltage. If I remove the grounding clamp from the table I get good live voltage. What am I doing wrong.
I can cut (not good see other thread) if I turn the THC Control off.
and cutting is having issues

What if “work clamp” is connected to the work piece?

same as if I was connecting to slats