Magento Error After Enable the Category Flat Data
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I have ennabled the **Category Flat Data** in admin panel System --> index management.
After enable the **Category Flat Data** my product positions are not working.
Also my product previous and next buttons are getting below error in product details page.

    Fatal error: Call to undefined method Mage_Catalog_Model_Resource_Eav_Mysql4_Category_Flat::getProductsPosition() in /var/domain/app/code/core/Mage/Catalog/Model/Category.php on line 308 

Right now i am using the magento ver. 1.5.1.0. 

So can any one help me? how to fix this issues? can any one suggest me the solution? 

Thanks

 