This is because the kernel that is packaged with this is pre knock on code. You will need to flash a kernel that is compatible and has the knock on code updated.
I don't found a v20y kdz... But I have an advice for you.
First, do a complete backup of your phone with TWRP if you are in v20... (sysem, data, efs, cache, etc.),
then flash with lg flashtool the v10k kdz (I think is the v10k or v10c, I dont know),
after that, update the phone via OTA until you are in v20y (cause the first update is to be in v20c, then you will be in v20k, and finally you'll be in v20y)
and finally root with stumproot for restore your backup (but only data, cache, and efs, because if you restore system the phone will brick, or bootloop)
Obviously for have a custom recovery, you will need use autorec for have it.
I got AT&T G2 with andriod 4.2 and unlocked it and rooted it using ioroot 10. I did 2 OTA update from AT&T and now my version showing 4.2.2 and Build # JDQ39B & Software version - D80010q.
I wanto now install this ROM D80020K. I read through entire forum and I figure out I need TWRP and KitKat BaseBand then I am good to go with this ROM. I have downlaoded KitKat baseband but I don't know how to update baseband from original Korea base band M8974A-AAAANAZM-1.0.190034.
Please help me with these :
1. Do I need to update baseband to KITKAT base band and if answer is yes then how should I do it. I have downloaded zip file.
2. How do I instal TWRP on my G2. Where to download files and guide to that.
3. After flashing this ROM how can I get my apps and data back. I don't want to loose my pics and apps that I havw now. I don't want to reinstall all apps again.
Please guide me .