Can't run Rails under Cygwin, due to LoadError: No such process from digest/md5

Question

In trying to run Rails under Cygwin, the ./script/server command is producing a load error that I can't find a solution for searching on Google. I can reproduce this error in irb as follows:

irb(main):001:0> require 'rubygems'
=> true
irb(main):002:0> require 'digest/md5'
LoadError: No such process - /usr/lib/ruby/1.8/i386-cygwin/digest/md5.so
        from /usr/lib/ruby/1.8/i386-cygwin/digest/md5.so
        from /usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:31:in `require'
        from (irb):2

$ ruby --version ruby 1.8.7 (2008-08-11 patchlevel 72) [i386-cygwin]

rails (2.3.8, 2.1.0) both fail with the same error

$ uname -a CYGWIN_NT-5.1 XXXXXX 1.5.25(0.156/4/2) 2007-12-14 19:21 i686 Cygwin