Wanhao D7 cannot lower build plate under the point it was upon startup


I’ve been attempting to lower my build plate using the “Execute Gcode” section on Photonic3D, but if I try to send a move command which would lower it below where it was when the printer was turned on, regardless of height, it fails to do so, and the message “movez:X:0.00 Y:0.00 Z:0.000 E:NAN” is printed in the text box underneath. The “Z:0.000” seems to represent what it believes to be my current Z position. I have tried to move it in both relative positioning and absolute positioning, and neither works.

Any ideas what could be going wrong?