caxlsx_rails: 0.4.0 generates file but can't be opened

I’m working with an extension of Spree 2.3. The method that generates the excel report is as follows:

def order_report
        export = !params[:q].nil?

        params[:q] ||= {}
        @show_only_completed = params[:q][:completed_at_not_null] == '1'
        params[:q][:s] ||= @show_only_completed ? 'completed_at desc' : 'created_at desc'

        # As date params are deleted if @show_only_completed, store
        # the original date so we can restore them into the params
        # after the search
        created_at_gt = params[:q][:created_at_gt]
        created_at_lt = params[:q][:created_at_lt]

        params[:q].delete(:inventory_units_shipment_id_null) if params[:q][:inventory_units_shipment_id_null] == "0"

        if !params[:q][:created_at_gt].blank?
          params[:q][:created_at_gt] = Time.zone.parse(params[:q][:created_at_gt]).beginning_of_day rescue ""
        end

        if !params[:q][:created_at_lt].blank?
          params[:q][:created_at_lt] = Time.zone.parse(params[:q][:created_at_lt]).end_of_day rescue ""
        end

        # Get the search parameters
        @search = Order.accessible_by(current_ability, :index).ransack(params[:q])

        # Restore dates
        params[:q][:created_at_gt] = created_at_gt
        params[:q][:created_at_lt] = created_at_lt
        render and return unless export

        @orders = @search.result(distinct: true) # TODO - make this a batch fetch

        # Put the orders into an Excel file
        render xlsx: "order_report", disposition: 'attachment', filename: 'order_report_' + Date.today.to_s + '.xlsx', xlsx_created_at: 0.days.ago

end

my template is called “order_report.xlsx.axlsx” and contains:

wb = xlsx_package.workbook

wb.add_worksheet(name: "Orders") do |sheet|

    titles =     [
        'Updated At',
        'Completed',
        'Order Number',
        'Name',
        'Address',
        'Phone',
        'Email',
        'Item',
        'url',
        'Quantity',
        'Order Total',
        'Status',
        'Shipping Status'
    ]

    sheet.add_row titles

    @orders.each do |order|
        first_row = true
        if order.line_items.any?
        order.line_items.each do |line_item|
            row = []

            row << (first_row ? order.updated_at : "")
            row << (first_row ? order.completed_at : "")
            row << (first_row ? order.number : "")
            if order.bill_address && first_row
                row << order.bill_address.full_name
                address_line = ""
                address_line << order.bill_address.address1 + " " if order.bill_address.address1?
                address_line << order.bill_address.address2 + " " if order.bill_address.address2?
                address_line << order.bill_address.city + " " if order.bill_address.city?
                address_line << order.bill_address.country.name + " " if order.bill_address.country_id?
                row << address_line
                row << (order.bill_address.phone? ? order.bill_address.phone : "")
            else
                row << ""
                row << ""
                row << ""
            end
            row << (first_row ? (order.email || "") : "")
            item = line_item.variant.name
            if line_item.product.individual_sale
                if line_item.material
                    item += " - " + line_item.material.name
                    item += " (" + line_item.material.options_text.gsub('&nbsp;', '') + ")" unless !line_item.material && line_item.material.option_values.empty?
                end
                if line_item.frame
                    item += " " + line_item.frame.name
                    item += " (" + line_item.frame.options_text.gsub('&nbsp;', '') + ")" unless line_item.frame.option_values.empty?
                end
                row << item 

                if line_item.product.photo_info
                    row << line_item.product.photo_info.image.url(:original)
                elsif (line_item.photo_src == 'bigstock') && !line_item.photo_key.blank?
                    if line_item.purchased_image
                        row << Bigstock::PurchasedImage.download_url(line_item.purchased_image.key)
                    else
                        row << "Bigstock image not purchased"
                    end
                elsif (line_item.photo_src == 'usrimg') && !line_item.photo_key.blank?
                    photo = UserPhoto.find_by_photo_hash line_item.photo_key
                    row << photo.photo.url(:original)
                else
                    row << (line_item.variant.images[0].attachment.url(:original)).to_s
                end
            else
                item += " (" + line_item.variant.options_text.gsub('&nbsp;', '') + ")" 
                row << item
                row << "" # cause there is no URL
            end

            row << line_item.quantity
            row << (first_row ? order.total.to_s : "")
            row << (first_row ? order.state.downcase.to_s : "")
            row << (first_row ? order.shipment_state.to_s : "")
            first_row = false
            sheet.add_row row
        end
        end
    end

end

The sheet generated using 0.3.0 using this exact code can be viewed at https://docs.google.com/a/grenadinetech.com/spreadsheets/d/17qV3gC23V-JR255_peZauy6WUBf1Ur5UJeUVD3tGPX8/edit?usp=sharing

I’ve had to version-lock the gem in order to continue developing the template on our extension. Any thoughts about what could have changed between versions to cause this error? Need any additional information?