I started to get this error today. I't was working without any problems to this day. But today I've lost connection and had to reboot whole device to make it work again.
I have network connection to ISP but in "Cellular" tab of lte1 interface i've got:
IMSI: +CME ERROR: 100
[admin@MikroTik] > /interface lte info lte1 once
pin-status: no password required
access-technology: Evolved 3G (LTE)
imsi: +CME ERROR: 100
subscriber-number: +CME ERROR: 100
I guess it can be related to network operator. I'm using it in passthrough mode with public IP.