What is a mobile network error on a Transport WR21?

I am getting an ERROR on a Transport WR21 device in the Management-Network Status>Interface>Mobile>Network:ERROR. I am also getting the following in the Mobile Statistics portion of the screen:
IP Address: Not Available
Primary DNS Address: Not Available
Secondary DNS Address: Not Available
Data Received: Not Available
Data Sent: Not Available

I have checked the configuration settings against another known working Transport WR21, and they are configured the same. Can someone tell me what the above information could possibly be caused by?

That could be caused by anything. Basically it is not getting an IP address so it could be SIM related (SIM PIN or failed SIM), it could be network related (wrong APN), it could be anything.

Are you registering on the cellular network at least?