Hjdcti

I found browsing the net a piece of code to allow groupable products instead of the table that showed by default to select quantities, have a dropdown menu to select an associate product.
I have in a grouped product, two associates, one simple and one virtual, if I choose the simple product via dropdown menu it goes fine, but if I choose the virtual one I get an error that tells me to indicate the quantity of the product.
It already states 1 in quantity, anyone could help me to fix the code?

Thanks a lot

The file path is: app/design/frontend/rwd/default/template/catalog/product/view/type/grouped.phtml

?>
<?php $this->setPreconfiguredValue(); ?>
<?php $_product = $this->getProduct(); ?>
<?php $_associatedProducts = $this->getAssociatedProducts(); ?>
<?php $_hasAssociatedProducts = count($_associatedProducts) > 0; ?>
<?php echo $this->getChildHtml('product_type_data_extra') ?>
<form action="<?php echo $this->getAddToCartUrl($_product) ?>" method="post" class="add-to-cart" id="product_addtocart_form_<?php echo $_product->getId()?>"<?php if($_product->getOptions()): ?> enctype="multipart/form-data"<?php endif; ?>>
<div style="float:right;border:1px solid;padding:5px; width: 100%;">
 <?php if($_product->isGrouped()): ?>
 <?php $_subAssociatedProducts = $_product->getTypeInstance(true)->getAssociatedProducts($_product); ?>
 <?php if(count($_subAssociatedProducts))?>
 <!--<div class="groupedTitle">Dimensiune / Grosime</div>-->
 <select id="grouped_products" name="grouped_products" onchange="addSuperQty('<?php echo $_product->getId()?>',this.value);">
 <?php foreach ($_subAssociatedProducts as $_item) ?>
 <option value="<?php echo $_item->getId()?>" id="<?php echo number_format($_item->getFinalPrice(),2); ?>"><?php echo $this->htmlEscape($_item->getName())?></option>
 <?php ?>
 </select>
 <?php ?>
 <span id="span_<?php echo $_product->getId()?>"></span>
 <input type="text" size="3" name="qty" onchange="changeQty(this.value,'<?php echo $_product->getId()?>');" id="<?php echo $_product->getId()?>_qty" maxlength="12" value="<?php echo $_item->getQty() * 1 ?>" class="input-text qty" />
 <?php else:?>
 <input type="text" size="3" name="qty" id="qty" maxlength="12" value="<?php echo $_item->getQty() * 1 ?>" class="input-text qty" />
 <?php endif; ?>

</div>
</form>
<script type="text/javascript">decorateTable('super-product-table')</script>