I am running merger tree on Enzo simulations following the recipe given in YT documentation. YT crashes by producing the following error. I am using yt version "b118390aa42c".  Any ideas what is going on here?

FOF CPU TIME: 2.408634 secs
========== Cycle 00009 (z=9.999997) ==========
Parent halo = 0
--> Most massive progenitor == Halo -1
========== Cycle 00008 (z=14.999989) ==========
========== Cycle 00007 (z=19.999992) ==========
========== Cycle 00006 (z=29.999961) ==========
Traceback (most recent call last):
  File "enzo.py", line 33, in <module>
    mt.save_halo_evolution('halos.h5')
  File "/home/uni05/mlatif/ytnew/yt-x86_64/src/yt-hg/yt/analysis_modules/halo_merger_tree/enzofof_merger_tree.py", line 507, in save_halo_evolution
    halo_id = self.levels[cycle_fin][0].halo_id
IndexError: list index out of range