Rails cannot connect error after updating using ruby and rails to slightly newer versions

I am on a mac. Have been developing using a manually installed
(according to the hivelogic instructions) ruby, rails, gems, mongrel
setup. Life was good.

When I noticed that my ruby version was out of date, I decided to
switch to using macports to maintain the software on my mac. I used it
to install a new ruby and gems, and then used gems to get the latest
rails. Life seemed to be good.

Next I ran mongrel to launch the app and it seems to start ok. But
when I go to localhost:3000 I get "cannot connect" from my browser.

If I create a hello world application (rails helloworld) and then go
to localhost:3000 then it does what is expected.

So:

I suspect there is some dependency in my rails app that stopped
working on something which changed when I updated my ruby and rails
install. Here is what *I know* changed:

- ruby and rails are now installed in /opt./local/bin where before it
was installed in /usr/local/bin ( I have updated my path of course -
to include opt first and usr second
- ruby and rails have slightly higher version numbers. Ruby from 1.8.4
to 1.8.6 and rails from 1.2.0 (I think) to 1.2.3

However I can't find a dependency on either of those things in my
rails application.

Any hints? Am I looking in totally the wrong place?

Ah yes, I think, but don't know how to interpret it. Can you help?

/mydev/rubywork/myscrum$ mongrel_rails start -d
/mydev/rubywork/myscrum$ mongrel_rails stop
!!! PID file log/mongrel.pid does not exist. Not running?
mongrel::stop reported an error. Use mongrel_rails mongrel::stop -h to
get help.

/mydev/rubywork/myscrum$ ls log
mongrel.log
/mydev/rubywork/myscrum$ cd log

/mydev/rubywork/myscrum/log$ cat mongrel.log
** Daemonized, any open files are closed. Look at log/mongrel.pid and
log/mongrel.log for info.
** Starting Mongrel listening at 0.0.0.0:3000
** Starting Rails with development environment...
/mydev/rubywork/myscrum/config/boot.rb:26: undefined method
`cleanpathhe' for Gem:Module (NoMethodError)
        from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/
custom_require.rb:27:in `gem_original_require'
        from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/
custom_require.rb:27:in `require'
        from /mydev/rubywork/myscrum/config/environment.rb:11
        from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/
custom_require.rb:27:in `gem_original_require'
        from /opt/local/lib/ruby/vendor_ruby/1.8/rubygems/
custom_require.rb:27:in `require'
        from /opt/local/lib/ruby/gems/1.8/gems/mongrel-1.0.1/lib/
mongrel/rails.rb:155:in `rails'
        from /opt/local/lib/ruby/gems/1.8/gems/mongrel-1.0.1/bin/
mongrel_rails:112:in `cloaker_'
        from /opt/local/lib/ruby/gems/1.8/gems/mongrel-1.0.1/lib/
mongrel/configurator.rb:138:in `call'
         ... 6 levels...
        from /opt/local/lib/ruby/gems/1.8/gems/mongrel-1.0.1/lib/
mongrel/command.rb:211:in `run'
        from /opt/local/lib/ruby/gems/1.8/gems/mongrel-1.0.1/bin/
mongrel_rails:243
        from /opt/local/bin/mongrel_rails:16:in `load'
        from /opt/local/bin/mongrel_rails:16
/mydev/rubywork/myscrum/log$

More info:

I located the line in boot.rb where the error was happening, and
copied the corresponding lines from the working hello world
application:

    if version = defined?(RAILS_GEM_VERSION) ? RAILS_GEM_VERSION :
rails_gem_version
      # Asking for 1.1.6 will give you 1.1.6.5206, if available --
makes it easier to use beta gems
      rails_gem = Gem.cache.search('rails', "~>#{version}.0").sort_by
{ |g| g.version.version }.last

Now I get into the home page but of course I don't know what other
problems are introduced, or what caused it, or how to do a proper
repair.

Any further info would be greatly appreciated!