WWW::Mechanize and Rails console not playing well

I can run this code just fine in irb, but when I run it in rails
script/console, I get an error:

res = agent.submit(search_form, search_form.buttons.first)

ArgumentError: one hash required
        from /home/jwoods/NetBeansProjects/activista/vendor/rails/
actionmailer/lib/../../actionpack/lib/../../activesupport/lib/
active_support/core_ext/string/interpolation.rb:85:in `%'
        from /usr/lib/ruby/1.8/webrick/httputils.rb:352:in `_escape'
        from /usr/lib/ruby/1.8/webrick/httputils.rb:352:in `gsub'
        from /usr/lib/ruby/1.8/webrick/httputils.rb:352:in `_escape'
        from /usr/lib/ruby/1.8/webrick/httputils.rb:370:in
`escape_form'
        from /usr/lib/ruby/1.8/www/mechanize/util.rb:9:in
`build_query_string'
        from /usr/lib/ruby/1.8/www/mechanize/util.rb:6:in `map'
        from /usr/lib/ruby/1.8/www/mechanize/util.rb:6:in
`build_query_string'
        from /usr/lib/ruby/1.8/www/mechanize/form.rb:199:in
`request_data'
        from /usr/lib/ruby/1.8/www/mechanize.rb:387:in `post_form'
        from /usr/lib/ruby/1.8/www/mechanize.rb:331:in `submit'
        from (irb):23

Here's the code:
#!/usr/local/bin/ruby
require 'rubygems'
require 'mechanize'
require 'logger'
require 'uri'
require 'net/http'

agent = WWW::Mechanize.new { |a| a.log = Logger.new(“mech.log”) }
agent.user_agent_alias = ‘Mac Safari’
page = agent.get(‘http://www.fyi.legis.state.tx.us/Address.aspx’)
search_form = page.form_with(:name => “AddressForm”)
search_form.field_with(:name => “Address1”).value = “501 W 26th St,
Apt 110”
search_form.field_with(:name => “City”).value = “Austin”
search_form.field_with(:name => “ZipCode”).value = “78705”
search_form.field_with(:name => “DistrictType”).options[0].select
res = agent.submit(search_form, search_form.buttons.first)

It should return a Mechanize page object.

And no, that's no longer my address.

What is this interpolation core extension? Why is that causing a
problem? Can I disable it for this lib I'm working on?

Thanks so much,
John