command-t vim "Could not load C extension"

Solution 1:

Pete, you must install ruby-dev package before invoke "rake make" command.

Solution 2:

Command-T requires a compiled C extension to work. Here's the relevant section from the Command-T homepage on how to compile the extension:

The C extension must also be then compiled; for instance, if Vimball installs
your plugin files in ~/.vim, then you would do this: 

  cd ~/.vim/ruby/command-t 
  ruby extconf.rb 
  make 

Note that Command-T requires a version of VIM with Ruby support enabled, and 
it must be compiled using the same version of Ruby that Vim itself links 
against. For more details see the documentation: 

    http://git.wincent.com/command-t.git/blob_plain/HEAD:/README.txt

Solution 3:

The thing that usually trips people up the most is that their Command-t has been compiled with a different version of Ruby than their Vim's version. In order do install Ruby and match the proper versions, you are going to want to install RVM and Ruby, install the correct version of Ruby, and do a rake make in the ~/.vim/bundle/Command-T plugin directory.

Here is a step-by-step guide to install Command-t.