Hi,
If tree is still in dev then try to simply activate and save it again without changing anything. This simple step has helped me a couple of times.
You need to carefully check modifications you've done in your Z format tree comparing to standard one. May be post screen-shots of your added or changed nodes or whatever modifications are here. If not, then the only way is, as suggested earlier, run program sapfpaym_schedule in foreground and debug.
best regards.