I didnt change the META-INF but i didnt faced any data mount error.
I booted into recovery and mount data , unmount system and cache and then mounted them again and flashed gapps and it worked fine. I can install apps from the playstore without any cache error.
strange - when ever I flashed the rom with the orig updater script I could no longer mount data afterwards maybe its just me
other people said they had problem with the playstore though so maybe they had same problem as me
anyway long as everything works no matter what method you use thats all that matters