Error when execute "script/generate rspec"

I want to use rspec in my new project, but when install rspec, error
occured. Could anyone help me? Thanks in advance.

Thanks for your reply.
I have just solved the probelm. It seems that it could find the right
gem.
There are gems in both /usr/local/lib/ruby/gems/1.8 and /home/
xxxxx/.gems,
I remove the /home/xxxxx/.gems and everything works ok.