Generate process give error

Dear MG5 Group,

I created a new model use Feynrules, everything works just fine, but when I try to generate a process it gives me error.

Defined multiparticle all = g a ve vm vt ve~ vm~ vt~ u c t d s b u~ c~ t~ d~ s~ b~ z w+ h xr w- e- mu- ta- xe- e+ mu+ ta+ xe+
MG5_aMC>generate xr xr > e+ e-
INFO: Checking for minimal orders which gives processes.
INFO: Please specify coupling orders to bypass this step.
Command "generate xr xr > e+ e-" interrupted with error:
KeyError : '1'
Please report this bug on https://bugs.launchpad.net/mg5amcnlo
More information is found in 'MG5_debug'.
Please attach this file to your report.

And here is what in MG5_debug

#************************************************************
#* MadGraph5_aMC@NLO *
#* *
#* * * *
#* * * * * *
#* * * * * 5 * * * * *
#* * * * * *
#* * * *
#* *
#* *
#* VERSION 2.6.1 2017-12-12 *
#* *
#* The MadGraph5_aMC@NLO Development Team - Find us at *
#* https://server06.fynu.ucl.ac.be/projects/madgraph *
#* *
#************************************************************
#* *
#* Command File for MadGraph5_aMC@NLO *
#* *
#* run as ./bin/mg5_aMC filename *
#* *
#************************************************************
set group_subprocesses Auto
set ignore_six_quark_processes False
set loop_optimized_output True
set loop_color_flows False
set gauge unitary
set complex_mass_scheme False
set max_npoint_for_channel 0
import model sm
define p = g u c d s u~ c~ d~ s~
define j = g u c d s u~ c~ d~ s~
define l+ = e+ mu+
define l- = e- mu-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
import model /home/xianhui/hep-soft/MG5_aMC_v2_6_1/models/DMS
generate xr xr > e+ e-
Traceback (most recent call last):
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/interface/extended_cmd.py", line 1467, in onecmd
    return self.onecmd_orig(line, **opt)
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/interface/extended_cmd.py", line 1421, in onecmd_orig
    return func(arg, **opt)
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/interface/master_interface.py", line 269, in do_generate
    return self.cmd.do_generate(self, line, *args, **opts)
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/interface/madgraph_interface.py", line 4446, in do_generate
    self.do_add(" ".join(args))
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/interface/master_interface.py", line 220, in do_add
    return self.cmd.do_add(self, line, *args, **opts)
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/interface/madgraph_interface.py", line 3079, in do_add
    optimize=optimize, diagram_filter=diagram_filter)
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/core/diagram_generation.py", line 1595, in __init__
    self.get('amplitudes')
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/core/diagram_generation.py", line 1643, in get
    diagram_filter=self['diagram_filter']))
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/core/diagram_generation.py", line 1672, in generate_multi_amplitudes
    diagram_filter))
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/core/diagram_generation.py", line 1913, in find_optimal_process_orders
    process_definition.get_minimum_WEIGHTED()
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/core/base_objects.py", line 3639, in get_minimum_WEIGHTED
    particles, hierarchy = model.get_particles_hierarchy()
  File "/home/xianhui/hep-soft/MG5_aMC_v2_6_1/madgraph/core/base_objects.py", line 1362, in get_particles_hierarchy
    k in coupling_orders])))
KeyError: '1'
                          MadGraph5_aMC@NLO Options
                          ----------------
        complex_mass_scheme : False
                      gauge : unitary
         group_subprocesses : Auto
  ignore_six_quark_processes : False
           loop_color_flows : False
      loop_optimized_output : True
  low_mem_multicore_nlo_generation : False
     max_npoint_for_channel : 0
               stdout_level : 20 (user set)

                         MadEvent Options
                          ----------------
     automatic_html_opening : False (user set)
                    nb_core : None
        notification_center : True
                   run_mode : 2

                      Configuration Options
                      ---------------------
                        OLP : MadLoop
                    amcfast : amcfast-config
                   applgrid : applgrid-config
                auto_update : 7
         cluster_local_path : None
           cluster_nb_retry : 1
              cluster_queue : None (user set)
         cluster_retry_wait : 300
               cluster_size : 100
      cluster_status_update : (600, 30)
          cluster_temp_path : None
               cluster_type : condor
                    collier : /home/xianhui/hep-soft/MG5_aMC_v2_6_1/HEPTools/lib (user set)
               cpp_compiler : None
             crash_on_error : False
               delphes_path : ./Delphes
                 eps_viewer : /usr/bin/evince (user set)
        exrootanalysis_path : ./ExRootAnalysis
              f2py_compiler : None
                    fastjet : None (user set)
           fortran_compiler : None
                      golem : /home/xianhui/hep-soft/MG5_aMC_v2_6_1/golem95/lib (user set)
                 hepmc_path : None (user set)
                  hwpp_path : None (user set)
                     lhapdf : /home/xianhui/hep-soft/MG5_aMC_v2_6_1/HEPTools/lhapdf6/bin/lhapdf-config (user set)
          madanalysis5_path : /home/xianhui/hep-soft/MG5_aMC_v2_6_1/HEPTools/madanalysis5/madanalysis5 (user set)
           madanalysis_path : ./MadAnalysis
  mg5amc_py8_interface_path : /home/xianhui/hep-soft/MG5_aMC_v2_6_1/HEPTools/MG5aMC_PY8_interface (user set)
                      ninja : /home/xianhui/hep-soft/MG5_aMC_v2_6_1/HEPTools/lib (user set)
        output_dependencies : external
                      pjfry : None (user set)
            pythia-pgs_path : ./pythia-pgs
               pythia8_path : /home/xianhui/hep-soft/MG5_aMC_v2_6_1/HEPTools/pythia8 (user set)
                    samurai : None
               syscalc_path : /home/xianhui/hep-soft/MG5_aMC_v2_6_1/SysCalc (user set)
                    td_path : ./td
                text_editor : None
                thepeg_path : None (user set)
                    timeout : 60
                web_browser : None

I don't know why this happen, Thank you a lot!

Best!
Charlie