[Grant]

Originally Posted by Zaja

Try to replace:

<input type="button" value="{$lng.lbl_add_to_cart}" onclick="document.orderform_{$products[product].productid}_{$products[product].add_date}.submit();"> 

with(not tested):

{if $config.General.unlimited_products ne "Y" and ($product.avail le 0 or $product.avail lt $product.min_amount)}
{$lng.txt_out_of_stock}
{else}
<input type="button" value="{$lng.lbl_add_to_cart}" onclick="document.orderform_{$products[product].productid}_{$products[product].add_date}.submit();"> 
{/if}

Oooppps! Now everything is out of stock?