Did you come from another nightly and if you did what all did you wipe before flashing? Also was the market and everything working before you flashed the new nightly? If you came from another nightly and had the market working before than you shouldn't need to reflash the Gapps. If you came from another nightly that had a working market I would suggest restoring a backup to that, if you have one which you should. Then wipe cache and dalvik then reflash the nightly #8. If that still doesn't fix it the you will need to a complete wipe (data, cache, dalvik) then flash #8 then flash gapps.