1 error(s) on assignment of multiparameter attributes

I am trying to create a form for processing credit cards. For the
credit card expiration date, I would like to leave the day field out
of the form for obvious reasons. However, the following code is
producing an error for me.

Any ideas?

Thanks!

<p><label for="email">Expiration</label><br/>
<input type="hidden" id="user_card_expiration_3i"
name="user[card_expiration(3i)]" value="1" />
<%= f.date_select(:card_expiration, :start_year =>
2008, :use_month_numbers => false,
                                    :discard_day =>
true, :include_blank => false) %></p>

ActiveRecord::MultiparameterAssignmentErrors in
AccountController#signup_unlimited

Parameters:

{"user"=>{"company_name"=>"",
"card_type"=>"Mastercard",
"password_confirmation"=>"",
"card_number"=>"",
"card_expiration(1i)"=>"2008",
"first_name"=>"",
"card_expiration(2i)"=>"2",
"last_name"=>"",
"login"=>"",
"password"=>"",
"card_expiration(3i)"=>"1",
"email"=>""},
"commit"=>"Sign up",
"authenticity_token"=>"c4952d3607e216e85ca0ca4b76eb65272d1f85f7"}

How about leaving the date field out altogether? Passing in just a month and a year should do the trick.

Makes sense, i could even make it one single drop down. How would i have the default selection be this years current month tho?

I was able to get rid of the error by converting the column to a Date Type instead of a String type.

Thanks!

Jason