Not familiar with this pen at all, but usually in the instruction manual there's a section on faults that the pen may develop, check the manual to see what it says.
Hi edgemac if you don't see anything in instructions I would give manufacturers a ring I use a nexus Rx meter and a nexus hct for testing ketones I've had a few problems in the past with these meters but one call to nexus and they tell me what's wrong or send me a replacement just a thought good luck.