Ever wonder what the easiest way to debug error coming out from VF01? Well, you could try creating watchpoint by checking SYS-MSGID = 'VF' but the easiest is to place a session breakpoint in subroutine VBFS_HINZUFUEGEN which can be found in INCLUDE LV60AA98.
All errors found in the log will need to go through the above routine. Hope this helps! I've been enjoying doing this stuff for more than 20 years! Hope you too! :)