SAP Note 12896 - Error message FM120 during dunning

Symptom:

The dunning run log contains the error message FM120: Account & & is blocked by dunning run &.The dunning run that is supposedly blocking this account doesn't exist.

Cause and prerequisites

An entry is still in lock table MAHNS.
An abnormal termination probably occurred during the dunning run
which was deleted without being analysed more closely.

Solution
Since the dunning run is no longer in the system, you cannot
analyse this problem. However, the unwanted entry in the
lock table can be deleted using the following auxiliary program:

REPORT ZFMAHNS.
tables: MAHNS.

DELETE FROM MAHNS
WHERE KOART = 'D' " <- or 'K' if vendor
and BUKRS = '0001' " <- appropriate company code
and KONKO = '1234567890' " <- account number with leading zeros
and LAUFD = 'JJJJMMTT'. " <- date of the blocking dunning run
" <- in internal format therefore
YYYYMMDD
IF SY-SUBRC = 0.
WRITE: ' Entry deleted '.
ELSE
WRITE: ' No Entry Found'
ENDIF.


Caution: It is important to protect this program from misuse and delete
it directly after using it.

Key word: F150