can't convert Class into String

(in response to an email from Lukas asking for more information)

In user.rb:

  acts_as_xapian :texts => [ :email, :name ],
                 :terms => [[:name, 'N', "name"], [:email, 'E', "email"]]

In advisor.rb:

  acts_as_xapian :texts => [ :all_emails, :name, :first_name, :last_name, :email_pattern, :program],
                 :terms => [[:name, 'N', "name"],
                            [:all_emails, 'A', "all_emails"],
                            [:first_name, 'F', "first_name"],
                            [:last_name, 'L', "last_name"],
                            [:email_pattern, 'P', 'email_pattern'],
                            [:program, 'U', 'program'],
                            [:state, 'S', 'state']]

We aren't calling a Xapian search; the error occurs when executing acts_as_xapian. The line number is always the last line of the terms assignment (i.e. [:state, ...]].)