title: Product Type is invalid or not supported in rows for custom product type
body: <p>I'm having Custom product type product in my Magento store like "bookable".so i try to import 3 product with "_type" value "bookable". It throw me the error </p>
  
  <pre><code>   Product Type is invalid or not supported in rows: 1, 2, 3
  </code></pre>
  
  <p>I found the validation i checked here in core</p>
  
  <p>app/code/core/Mage/importexport/Model/import/Entity/Product.php</p>
  
  <p>line around 1439. </p>
  
  <p>How can i solve this problem</p>
  
  <p>Thanks in advance</p>