When trying to mark order as "Send", this message appears

[phonodk]

SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`phonodk_magento`.`pdmerp_inventory_warehouse_order`, CONSTRAINT `fk_erp_inventory_warehouse_order_erp_inventory_warehouse1` FOREIGN KEY (`warehouse_id`) REFERENCES `pdmerp_inventory_warehouse), query was: INSERT INTO `pdmerp_inventory_warehouse_order` (`qty`) VALUES (?)

What do i do?

[Pronto]

These tables you referenced are not Magento tables. Apparently there's an issue with ERP integration -- the system is trying to create duplicate records to a table with unique constraint. This might be because bad recovery, bug in extension of because somebody messed around in databases or because MySQL error. You're guess is as good as mine.