how to save string datetime to datetime field in database?

im using rails 3 app. and i cant save my datetime value from my datetime picker to my database in sql server 2005. i keep getting invalid date. any suggestions?

i have this in my model:

scope :available, lambda {
|checkin, checkout| { 
  :select => 'amenities.*',
  :order => 'id',
  :conditions => ["
    amenities.id NOT IN 
    (
      SELECT aa.id from amenities aa, amenity_list al WHERE
      aa.id = al.amenities_id AND
      (
        (? BETWEEN al.checkin AND al.checkout) OR
        (? BETWEEN al.checkin AND al.checkout)
      )
    )", 
    checkin, checkout 
 开发者_JAVA技巧 ] 
 }
}

here's my controller:

def step2
    @cart = current_cart    

    checkin = params[:checkin]
    checkout = params[:checkout]
    @amenities = Amenity.available(checkin, checkout)

    session[:checkin] = checkin
    session[:checkout] = checkout
end

application.js

$(function() {
    var dates = $( "#checkin, #checkout" ).datetimepicker({
        dateFormat: 'mm/dd/yyyy hh:MM:ss TT',
        buttonImageOnly: true,
        buttonImage: 'images/icons/cal.png',
        showOn: 'button',
        showAnim: 'blind',
        defaultDate: "+1w",
        changeMonth: false,
        numberOfMonths: 2,
        minDate: new Date(),
        onSelect: function( selectedDate ) {
            var option = this.id == "checkin" ? "minDate" : "maxDate",
                instance = $( this ).data( "datetimepicker" ),
                date = $.datetimepicker.parseDate(
                    instance.settings.dateFormat ||
                    $.datetimepicker._defaults.dateFormat,
                    selectedDate, instance.settings );
            dates.not( this ).datetimepicker( "option", option, date );
        }
    });
});

Have you tried Date.parse(checkin) ?