Rails 2.3.1 rack error in Ruby 1.9.1

[2009-03-06 10:03:59] ERROR NoMethodError: undefined method `each' for #<String:0x34aaf1c>
	/usr/local/lib/ruby191/gems/1.9.1/gems/actionpack-2.3.1/lib/action_controller/vendor/rack-1.0/rack/handler/webrick.rb:52:in `service'
	/usr/local/lib/ruby191/1.9.1/webrick/httpserver.rb:111:in `service'
	/usr/local/lib/ruby191/1.9.1/webrick/httpserver.rb:70:in `run'
	/usr/local/lib/ruby191/1.9.1/webrick/server.rb:183:in `block in start_thread'

This was caused by trying to render a TemplateError due to a problem in my app:

ActionView::TemplateError (incompatible character encodings: ASCII-8BIT and UTF-8) on line #56 of app/views/tracks/show.html.erb:
53: 			<p><%= @pictures %></p>
54: 		<% else %>
55: 			<ul style="list-style-type: none; padding: 0; margin: 0;">
56: 			<%= render :partial => 'picture', :collection => @pictures %>
57: 			</ul>
58: 		<% end %>
59: 	</div>

    app/views/tracks/show.html.erb:56:in `concat'
    app/views/tracks/show.html.erb:56
    /usr/local/lib/ruby191/1.9.1/webrick/httpserver.rb:111:in `service'
    /usr/local/lib/ruby191/1.9.1/webrick/httpserver.rb:70:in `run'
    /usr/local/lib/ruby191/1.9.1/webrick/server.rb:183:in `block in start_thread'