Could not find libv8-3.16.14.9 in any of the sources

Problem

You are trying to upgrade one of your gems (ie uglifier) and at the same time you are using a new gemset (ie for rails 4.2.4), and you get the following error when you are trying to bundle:

Solution

Upgrade to rails 4.2.4 first and bundle and afterwards change the other gem and do bundle again.

libv8 error in new rails installation

Problem

You are getting a libv8 installation error in a new rails 4.0 application in an older linux installation

Solution

This is causes by the latest gem version of the therubyracer dependency on the libv8.
You can get over it by specifying version 0.11.4 for the gem as in:

and then running bundle install again.