z to tau pair with lep-had decay fails

Dear all,

I've been running into some problems trying to simulate Z->tautau events, with one tau decaying leptonically and the other hadronically. This is using Madgraph5_aMC@NLO version 2.3.3.

The process I've been trying to generate is the following:
p p > z, (z > ta+ ta-, ta+ > l+ vl vt~, ta- > vt j j )
When trying to run this with MG5 defaults, the execution gets as far as "improving channels", then after a delay fails with
'''
At line 719 of file dsample.f (unit = 25, file = 'ftn25')
Fortran runtime error: End of file
ERROR DETECTED
'''
and no event output is generated (see full log pasted below).
The cross-sections shown below are very small, I believe because of the default zero tau width. importing model sm-lepton_masses (which includes the proper tau width) does not seem to fix the failure.

Either the leptonic or hadronic decay alone are generated without problems (leaving an undecayed +/-15 in the output .lhe). This failure only seems to arise when attempting to do both at once.

Bizarrely, if the Z is allowed to be off-shell using "pp > z > ta+ ta-", the lep-had decay is generated without any problems.

Since I'm only really interested in the decay of the Z, I tried generating
z > ta+ ta-, (ta+ > l+ vl vt~, ta- > vt j j )
This has the same failure as the above. Likewise the leptonic or hadronic decays alone are successful, showing a stationary Z in the event record.

I can't work out whether there is some problem with my syntax, whether I'm asking something unreasonable of MG, or whether this is a genuine problem.
Any help you can offer would be very much appreciated!
Ben

'''
Generating 10000 events with run name run_01
survey run_01
INFO: compile directory
compile Source Directory
Using random number seed offset = 21
INFO: Running Survey
Working on SubProcesses
INFO: P1_qq_z_z_taptam_tap_lvlvl_tam_vlqq
INFO: Idle: 0, Running: 1, Completed: -1
/var/clus/usera/brunt/MG5_aMC_v2_3_3/runs/20160531_testing_for_MG_forum/SubProcesses/survey.sh run in 2.850373 s
/var/clus/usera/brunt/MG5_aMC_v2_3_3/runs/20160531_testing_for_MG_forum/SubProcesses/survey.sh run in 1.734886 s
INFO: Idle: 0, Running: 1, Completed: -1
/var/clus/usera/brunt/MG5_aMC_v2_3_3/runs/20160531_testing_for_MG_forum/SubProcesses/survey.sh run in 0.636168 s
INFO: End survey
refine 10000
INFO: Refine results to 10000
/var/clus/usera/brunt/MG5_aMC_v2_3_3/madgraph/madevent/gen_ximprove.py:746: DeprecationWarning: object.__new__() takes no parameters
  return super(gen_ximprove, cls).__new__(gen_ximprove_v4, cmd, opt)
/var/clus/usera/brunt/MG5_aMC_v2_3_3/madgraph/madevent/gen_ximprove.py:752: DeprecationWarning: object.__init__() takes no parameters
  super(gen_ximprove, self).__init__(cmd, opt)
INFO: Generating 10000.0 unweigthed events.
INFO: Effective Luminosity 2.01447399566e+15 pb^-1
INFO: need to improve 3 channels
Current estimate of cross-section: 5.95689e-12 +- 3.87936468257e-12
    P1_qq_z_z_taptam_tap_lvlvl_tam_vlqq
At line 719 of file dsample.f (unit = 25, file = 'ftn25')
Fortran runtime error: End of file
ERROR DETECTED
ajob1 run in 74.207109 s
INFO: Idle: 11, Running: 1, Completed: 1
At line 719 of file dsample.f (unit = 25, file = 'ftn25')
Fortran runtime error: End of file
ERROR DETECTED
ajob3 run in 68.949863 s
INFO: Idle: 10, Running: 1, Completed: 2
At line 719 of file dsample.f (unit = 25, file = 'ftn25')
Fortran runtime error: End of file
ERROR DETECTED
'''