Diagnosis
The net outpayment amount could not be determined since the outpaymentcommitment account in a document line (VDBEPI) was incorrectly set.
Technical description with the help of an example in order to finderrors:
For loans given, the outpayment commitment account, e.g. acct0000153339 is contained in VDBEPI_RHABEN (VDBEPI-SBEWZITI = 'A') in theactual outpayment record.
The outpayment commitment account 0000153339 must, on the other hand beVDBEPI-RSOLL for a discount withholding record (this refers to thecredit item created for the withholding within the discount record)since the withholding record reduces the outpayment amount.
In VDBEPI the relevant fields are, for example filled as follows:
SBEWZITI SBEWART JEINBEHALT SSOLHAB RSOLL RHABEN
A |0001 | |S |0000046020 |0000153339
TA |1301 |X |S |0000153321 |0000099000
TA |3301 | |H |0000153339 |0000153321
If the withholding record increases the outpayment amount, e.g. apremium, the outpayment commitment account would in that case, have tobe in VDBEPI-RHABEN.
If the outpayment commitment account is in VDBEPI-RHABEN instead of inVDBEPI-RSOLL (or vice-versa) due to incorrect account determination,the net amount cannot be determined in the outpayment.
(It is not possible to determine the net amount via the recordsVDBEPI-JEINBEHALT = 'X', since no corresponding record with the set flagVDBEPI-JEINBEHALT is available for the overdue items selected forwithholding in the document but the amount reduces the net outpaymentamount.)

Procedure
Check you account determination and customizing settings.