Simple Captcha setup problem

Zhenning Guan wrote:

$ rake simple_captcha:setup
rake aborted! cannot open shared object file: No such file or
directory - /usr/lib/ruby/site_ruby/1.8/x86_64-linux/

(See full trace by running task with --trace)

how can I fix it?

This is because it is unable to find the library files. The best thing
to do would be to login as root and issue

ldconfig /usr/lib

alternatively, try exporting the path of libs to current path