UFO with Majorana fermions

Hi,

I'm using v2.8.3, which I understood has support for Majorana fermions, trying to generate a process i a model with some heavy majorana neutrinos.
I'm using the UFO at https://feynrules.irmp.ucl.ac.be/raw-attachment/wiki/HeavyN/SM_HeavyN_CKM_AllMasses_LO.tgz
(linked from the page https://feynrules.irmp.ucl.ac.be/wiki/HeavyN )

So far I have no success; details below. I guess some rookie mistake...
any help/hints much appreciated.

Cheers, Daniel.

----------------------------------------
sindarin file :

?vis_history = false
model = SM_HeavyN_CKM_AllMasses_LO (ufo)
process testHN = "e-" , "e+" => "mu-" , "mu+"
beams = "e-" , "e+"
sqrts = 250 GeV
beams_pol_density = @(-1), @(+1)
beams_pol_fraction = 100%, 100%
n_events = 50
sample_format = lcio
integrate (testHN) {
iterations = 10:500:"gw",10:500:"g",10:500:"w",10:500:"gw"
}
simulate (testHN)

--------------------------------
output:
.
.
| Model: Generating model 'SM_HeavyN_CKM_AllMasses_LO' from UFO sources
| Model: Searching for UFO sources in working directory
| Model: Found UFO sources for model 'SM_HeavyN_CKM_AllMasses_LO'
O'Mega: found Majorana fermions!
O'Mega: falling back to the Majorana representation for all fermions.
| Model: Model file 'SM_HeavyN_CKM_AllMasses_LO.ufo.mdl' generated
| Reading model file 'SM_HeavyN_CKM_AllMasses_LO.ufo.mdl'
?vis_history = false
| Switching to model 'SM_HeavyN_CKM_AllMasses_LO' (generated from UFO source)
.
.
[1/1] e- e+ -> mu- mu+ ...O'Mega: found Majorana fermions: use a supporting binary!
SUMMARY: 0 vertices
.
.
Warning: Process 'testHN': matrix element vanishes