<p>I have an <em>extremely</em> simple <code>routes.rb</code> in my Rails app:</p>

<pre><code>ActionController::Routing::Routes.draw do |map|
  map.resources :tags
end
</code></pre>

<p>Starting up my app with <code>script/server</code> and pointing my browser to <code>localhost:3000/tags/</code> yields:</p>

<h3>ActionController::MethodNotAllowed</h3>

<pre><code>Only get and post requests are allowed.
</code></pre>

<p>...</p>

<p>Starting up my app with <code>script/server webrick</code>, however, solves the problem.</p>

<p><em>Later</em>: in case it matters, I'm running Mongrel 1.1.5 on OSX 10.5.5.</p>

I have seen this happen with older versions of mongrel, but 1.1.5 is not old. I have also seen some similar problems when the browser double-posts a request to a URL. Is that happening here?
I'd need some more information to be able to help you: What browser are you using? Are you using the firebug plugin on Firefox? What does the server log say about the request, other than the MethodNotAllowed exception?