Default SIM error

My Optimus was gathering dust for like 4-5 months now. Today I thought of using it but when I inserted the SIM, it said "SIM error - Missing or Invalid SIM". I have been using the same SIM before in optimus too and was working just fine.
I don't remember but I think I did updated the OS and didn't check if the SIM was working or not.
Current OS: 7.10.8107.79

Here's a thing. I restored it back to an earlier backup and the SIM was working again. I then factory reset it and got the SIM error again.
Now I restored to the same backup and the SIM is no longer detected, I have no idea why.
Any help would be much appreciated.

Thanks

credits - robgee789