about Invoice split

question: Sometime while creating the invoice, the invoice get split and in split analysis it give the below error:
"Number of foreign trade data i" is different.

answer:

Plese refer the OSS note 11162, according to which, all the header fields
(table VBRK) are splitting criteria. So VBRK-EXNUM is also
a splitting criteria. The only possibility is to make that the system
sets the same EXNUM in the invoice.

Please check the field Determination of export data (TVCPF-EXPIM)
in the copy control Delivery -> Invoice at header level (transaction
VTFL)at the header level. Please check if it is set to
'B' if you do not want a split based on export indicator or export
segment number.

In a standard scenario the blank value is used.
There is, in the delivery header table LIKP, a field called EXNUM. This
is the key between the FT tables EIKP and EIPO (header and item, respec-
tively) and LIKP, as the FT info is not stored on the delivery itself.
When the delivery is created, the system does a check (country code of
the shipping plant vs. country code of the ship-to party). If the check
is not equal the FT routines kick-in and an EXNUM is assigned and the
values are transferred to EIKP and EIPO using EXNUM as the key.

When the invoice is created, the system looks at the value of EXPIM in
VTFL. If it is blank, the system refers to the same EXNUM for the FT
data in the invoice (similar scenario as the delivery, however, the
EXNUM from LIKP is moved to VBRK but it points to the same entries).

If the value 'A' is used, then the contents of fields to which EXNUM
points are copied but given a new EXNUM stored in VBRK (this is used to
avoid an invoice split when combining deliveries).

If the value 'B' is used, the the system knows that EXNUM from the
source document is to be ignored and the systems runs the FT routines to
read the values anew from customizing.

Also see note 36864 for more information.