I was having an issue with new Rails installs, the ruby gems bundle install would abort when it tried to install json gem (Installing json (1.7.6) with native extensions) along with the following error message:
The problem was that bundle install tries to download all new versions of gems, and since I already had json 1.7.6 installed, it threw an error when it got to that gem.
In order to exclude already installed gems, simply use
bundle install --local
This should let your install complete successfully.