You need to wipe data, cache, system. (If coming from a stock based ROM you actually need to format data). Then install ROM and gapps in that order without booting in between.
I suspect you are trying to install gapps after booting (or not wiping the data partition).
Guys the problem was the G Apps packages. The latest build that I downloaded, jsut dont installed Google Play Services for any reason. I tried with another build and it worked.