rspec error 'report_activate_error': Could not find RubyGem rspec-core (>=0) (Gem:LoadError)

I have a seemingly simple error but I can't seem to figure out what to do to resolve it. I have tried uninstalling and reinstalling but that hasn't helped me out. I am new to the terminal and to ruby/ruby on rails, so forgive my potentially stupid question. Does anyone know how to resolve this issue?

This is the exact error message I get when I try to run rspec.

/opt/local/lib/ruby/vendor_ruby/1.开发者_如何学编程8/rubygems.rb:827:in report_activate_error': Could not find RubyGem rspec-core (>= 0) (Gem::LoadError) from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems.rb:261:inactivate' from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems.rb:68:in `gem' from /usr/local/bin/rspec:18

Any help would be greatly appreciated. I am currently doing the RoR tutorial and can't get this to work...

Thanks in advance!