I tried the exact same thing. Downloaded cm-11-20140510-NIGHTLY-d800.zip from Cyanogenmod, moved it to my internal storage on my LG G2, tried flashing it, and it fails to flash. I of course factory reset my phone before trying to flash. I also downloaded the latest gapps and moved in to my phone, and that did not work either.
WARNING: Always create a backup of your ROM before factory resetting your phone, it has saved me plenty of times.
Links used:
CM DOWNLOADS -
https://download.cyanogenmod.org/?device=d800
GAPPS -
Google Apps - CyanogenMod