Update:
the eventmachine gem is installed and in my gemfile:
eventmachine (1.0.0, 0.12.10)
Please help! T
Someone kind of answered in comments...see below.
Basically though I had seperate versions of Ruby, which was getting confusing because some gems were only installed on certain versions of ruby.
Fix was totally uninstalling ruby and rails, then reinstalling. Fixed it!
This helped:
This comment in another thread seems promising for your issue. Can you ensure that you have "gem eventmachine" or similar in your Gemfile, and can successfully bundle? – Scott Helm Jan 6 at 6:24