I have a Configurable Product which has many Simple Products as variations of it. Some of the Simple Products are Out of Stock however when selected in the product listing, the product still displays as In Stock. What is causing this?
1). A Configurable Product is essentially a collection of Simple products which are presented as options in drop-down lists.
2). The drop-down list values are based on Attributes that must be set up in advance with required settings. The attribute Scope must be set to Global, and Use to Create Configurable Product must be True. The drop-down Attributes must be included in an Attribute Set, which is then used as a template for the Configurable Product.
3). The Simple products associated with a Configurable Product cannot include Custom Variants or Options, and must be based on the same Attribute Set that is used to create the Configurable product. The associated products can be generated automatically from inside with Configurable product record.
Note : Hope this helps http://www.magentocommerce.com/boards/viewthread/5204/
It sounds like perhaps your stock index is out-of-date. You can try manually reindexing via the System > Index Management. Or you can run it on the command line:
php -f /path/to/your/magento/shell/indexer.php -- --reindex cataloginventory_stock
It may also be a symptom of an outdated cache entry. You can rebuild the cache manually via System > Cache Management.