Order duplicated: SQLSTATE [23000]: Integrity constraint violation: 1062 Duplicate entry ‘T000082...

solution It is a bug in Magento 1.6.x and 1.7.x versions, and possibly other versions. The solution is as follows.
Copy the file / app / code / core / Mage / Sales / Model / Resource / Quote.php to / app / code / local / Mage / Sales / Model / Resource / Quote.php.
Change the line into the new file: $ bind = array (’: increment_id’ => (int) $ orderIncrementId); to: $ bind = array (’: increment_id’ => $ orderIncrementId);
Make sure that the compiler is refreshed (if used). Go to System> Tools> Compilation and click Run Compilation Process. thats it