Error When Create Drupal Commerce Product Display I have managed to create a product type and import my product data, so I now have a list of products. 
then i follow ryan szrama instruction http://drupalwatchdog.com/1/1/building-commerce-product-display

After that i get this error.
EntityMetadataWrapperException: Unknown data property commerce_product. in EntityStructureWrapper->getPropertyInfo() (line 339 of C:\xampp\htdocs\drupal7\modules\entity\includes\entity.wrapper.inc).

what i should do??
This in a known bug, you should either start fresh or use the Commerce repair. The problem is most likely that a field that was expected wasn't installed properly. This could happen if you add hook_line_item_info to a module that's enabled.