Checked why the back order has value, as per checking, the PO number does overflow into the back order number. The PO order maximum length is 6 digits only, but the PO number shown in the process is 8 digits and there are two digits added in the PO number at the beginning PO number. The added digits are 2 and 1 but before these two digits are added, the zero is added first then the 21 remove the zero at the beginning of the PO number. Though check the process, there are no functions or nothing included in it that is adding digits at the beginning of the PO number. Executed the process again, and check one by one process, as per checking, at the beginning of the execution, it is executing well, but after five to 8 PO created, there are invalid option errors, when this appears the next PO number to be processed is overflowing in the back order number. Checked the cause of the error, why it is being encountered.