I'm also getting the updater error 2 when trying to install the BTTF-BETA2 Nougat kernel (MD5 verified) on my LS997. Tried TWRP 3.2.3.4, 3.3.0.0, and 3.3.1.0.Well I ran into install error as well. On older TWRP also. 3.2.3.? I think lol. Anyway. Could be just a bad zipping of file (happens to me sometimes). Could you possibly try to fix and repost. Thank you again. LS997 btw.
The 2.2-BETA 38 Oreo kernel installed fine on my H918 in TWRP 3.3.1.0, by the way.