I got that error message when I installed httpclient on Ubuntu 10.04. The gem got installed the error is due to the rdoc. You can turn off the installation of rdoc by appending no rdoc switch to the .gemrc file :
echo 'gem: --no-ri --no-rdoc' >> ~/.gemrc
The above command will append the 'gem: --no-ri --no-rdoc' to your .gemrc file.
