Can't install a ruby gem because of an error?

Hey there, trying to install a ruby gem but I keep getting the following error:

ERROR:failed to build gem native extension

/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb
mkmf.rb can't find header files for ruby at/System/
Library/Frameworks/Ruby.framework/开发者_开发技巧Versions/1.8/usr/lib/ruby/ruby.h

I'm not exactly sure what is happening here. Is there anyone that knows what is going on and how to fix it?

Thanks!

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See : gem install mysql failure in Snow Leopard