You can also ensure your PATH ends up in the crontab, by putting the following at the top of the schedule.rb file:
env :PATH, ENV['PATH']
https://groups.google.com/forum/#!msg/whenever-gem/yRLt3f2jrfU/Exu3xfCo8DAJ
If above solution don’t work for you, try:
env :GEM_PATH, ENV['GEM_PATH']