The problem is

The order entry exists in the sales_flat_order_grid table but missing in sales_flat_order table

The solution is

Delete the entries from sales_flat_order_grid table which has no reference in sales_flat_order table

Run this SQL Query in your database:

DELETE FROM `sales_flat_order_grid`  
WHERE entity_id NOT IN (
   SELECT `entity_id` FROM `sales_flat_order`
);
invoices、shipments、creditmemos后台删除

DELETE FROM `sales_flat_invoice_grid`  
WHERE entity_id NOT IN (
   SELECT `entity_id` FROM `sales_flat_invoice`
);

DELETE FROM `sales_flat_shipment_grid`  
WHERE entity_id NOT IN (
   SELECT `entity_id` FROM `sales_flat_shipment`
);

DELETE FROM `sales_flat_creditmemo_grid`  
WHERE entity_id NOT IN (
   SELECT `entity_id` FROM `sales_flat_creditmemo`
);
后台展示的列表对应的数据表 sales_flat_order_grid、sales_flat_invoice_grid、sales_flat_shipment_grid、sales_flat_creditmemo_grid