Sorry to say, we had an oops on the first run of production boards. Solder mask was applied to the ground terminals for the board and EMP detector as well as J2, the EMP sensor jack.
Using a hobby knife or Dremmel tool, carefully remove the mask from these three areas. Note that the corner mounting holes that serve as grounds must have the mask removed from both the top and bottom of the pads. The mask only needs to be removed from the bottom of the board for J2. These pads are circled in the layout below. Note that the drawing shows the board as viewed from the top with only the bottom traces shown.
When you are done, you may wish to lightly tin these areas.