#6 error after I click 'start' to get data

[Jim]

It seems to find the light stone just fine, then when I
click the 'start' button, it gets the following error:

Looking for LightStone.
Found LightStone.Error in ThreadRead().
System.NullReferenceException: Object reference not
set to an instance of an object.
at Lightstone.USBlightstone.getSample()
at lsmApp.lsm.LightStone_READThreadMethod()

and nothing happens with the displays, and it won't stop
when I click 'stop'.