no such file to load - ftools,该怎么解决

2013-01-04

no such file to load -- ftoolsinternal:lib/rubygems/custom_require:29:in `require: no such file

no such file to load -- ftools
<internal:lib/rubygems/custom_require>:29:in `require': no such file to load -- ftools (LoadError)
from <internal:lib/rubygems/custom_require>:29:in `require'
from ./configure.rb:62:in `<main>'

这是什么问题啊，求解，求答案。谢谢
[解决办法]
#gem install ftool