Where can I edit store_id column?

[sasoriza]

trafficstars

For some reason I have to include this line 'filter_index' => 'main_table.store_id', within $this->addColumn('store_id', array( in app\code\local\Mage\Adminhtml\Block\Sales\Order\Grid.php, otherwise I am getting this error when filtering by store:

Integrity constraint violation: 1052 Column 'store_name' in where clause is ambiguous, query was: SELECT COUNT(*) FROM sales_flat_order_grid AS main_table INNER JOIN sales_flat_order AS order ON order.entity_id = main_table.entity_id WHERE (store_name = '1')

Where can I add this line if using this extension?