Gem install can not work in Cygwin Ruby1.9?

$ ruby -v
ruby 1.9.0 (2007-12-25 revision 14709) [i386-cygwin]

‘gem install **’ will raise Timeout::Error forever in Cygwin Ruby1.9!

ERROR: While executing gem … (Gem::RemoteFetcher::FetchError)
execution expired (Timeout::Error)
getting size of http://gems.rubyforge.org/Marshal.4.8

However,I can get ‘http://gems.rubyforge.org/Marshal.4.8’ quickly use
some code in irb:
irb(main):001:0> require ‘net/http’
=> true
irb(main):002:0> http = Net::HTTP.new(‘gems.rubyforge.org’,80)
=> #<Net::HTTP gems.rubyforge.org:80 open=false>
irb(main):003:0> request = Net::HTTP::Head.new(‘/Marshal.4.8’)
=> #<Net::HTTP::Head HEAD>
irb(main):004:0> resp = http.request request
=> #<Net::HTTPOK 200 OK readbody=true>

‘gem install **’ will work fine both in my windows Ruby1.9 and in Ubuntu
Ruby1.9,and they are all compiled from the same source.
I have try more than 20 times,and ‘gem install **’ will raise
Timeout::Error forever,how can I resolve it?