If you are receiving the following error message when trying to update Rails in NetBeans 6.7:

ERROR: While executing gem … (Gem::RemoteFetcher::FetchError) SystemCallError: Unknown error – An established connection was aborted by the software in your host machine (http://gems.rubyforge.org/gems/actionmailer-2.3.3.gem)

…try momentarily disabling your firewall. In my case, Windows Firewall seemed to be torpedoing the process: after disabling it for a moment, the update went through perfectly.

Perhaps obvious, but also easily overlooked.

Credit: This post by “joseph george” reminded me to check the firewall settings.