Warning while syncronising first time

Hello guys,

my problem was that the "add to cart" link in produkt view was missing. I looked into database and saw, that the value for "field_stock_availability_value" in "content_type_product" table was null. So I reinstalled all Magento modules in drupal. While syncronising the first time after reinstallation, this php warning occures:

warning: Invalid argument supplied for foreach() in C:\xampp\htdocs\projects\dev\www.mypage.de\htdocs\sites\all\modules\magento\magento_products\magento_products.module on line 236.

The value for "field_stock_availability_value" is null again. Have I missed somthing, or is this a bug?

Greetz
dops