Nighthawk M1 Mobile Broadband Disconnected

I recently purcase an unlocked Nighthawk M1 (M1100) broadband router that was from Amazon, hoping it would help with connectivity in my rural home.  I have tried two seperate AT&T sim cards in it, and both give the error "Mobile Broadband Disconnected", and are unable to connect to the internet.  Both sim cards are able to connect to the internet when used in other devices, so it does not seem to be a sim card issue, or a service issue, but a hardware issue.   

I have tried a factory reset, but that did not fix the issue.  Has anyone experienced this when trying to set up a new device?  Any suggested fixes?  Thank you.