Displaced Decay from Mesons

Hello,

I am interested in generating dark photons from meson decay, followed a displaced decay of the dark photon to electrons. What is the correct syntax to generate this process? I've tried to different ways so far and both were unsuccessful.

My first attempt was:
generate production pi0 > a y1
decay y1 > e+ e-
add process displace_decay y1
output

This results in the error message: IOError : [Errno 2] No such file or directory: 'Runs/DP_FromPions_Decay_2/Displaced_Decay/Events/run_01/unweighted_events.lhe.gz'

This error is strange because when I look in the "Displaced_Decay/Events/run_01" folder I see the lhe.gz file there. I'm not sure what's going on here.

My second attempt was
decay pi0 > a y1
decay y1 > e+ e-
add process displace_decay y1
output

This seemed to work: MadDump generated displaced decay events. However, when I look at the LHE file, I don't see any electrons in the event record. A single event looks like it has multiple pi0 > a y1 processes. Here is an example of a particular event in the LHE file.

<event>
16 0 +0.0000000e+00 0.00000000e+00 0.00000000e+00 0.00000000e+00
        0 -1 0 0 0 0 +0.0000000000e+00 +0.0000000000e+00 +0.0000000000e+00 0.0000000000e+00 0.0000000000e+00 0.0000e+00 9.0000e+00
      111 2 1 1 0 0 -2.1038312778e-01 -5.8363335628e-01 +5.4372126355e+01 5.4375833170e+01 1.3498000000e-01 0.0000e+00 0.0000e+00
       22 1 2 2 0 0 -6.1684301362e-02 -1.2619456421e-01 +9.9812953779e+00 9.9822836787e+00 0.0000000000e+00 0.0000e+00 -1.0000e+00
  5000001 1 2 2 0 0 -1.4869882641e-01 -4.5743879205e-01 +4.4390830977e+01 4.4393549491e+01 1.0000000000e-01 0.0000e+00 -1.0000e+00
      111 2 1 1 0 0 +1.4148633980e-01 -6.4280502446e-02 +2.6162779565e+01 2.6163589290e+01 1.3498000000e-01 0.0000e+00 0.0000e+00
       22 1 5 5 0 0 +1.3653683840e-03 -2.9840934764e-02 +4.4254373730e+00 4.4255381919e+00 0.0000000000e+00 0.0000e+00 1.0000e+00
  5000001 1 5 5 0 0 +1.4012097141e-01 -3.4439567683e-02 +2.1737342192e+01 2.1738051098e+01 1.0000000000e-01 0.0000e+00 1.0000e+00
      111 2 1 1 0 0 +2.8256356119e-01 +5.2209653077e-01 +1.0750525381e+00 1.2354693495e+00 1.3498000000e-01 0.0000e+00 0.0000e+00
       22 1 8 8 0 0 +1.0493452697e-01 +1.6993029200e-01 +3.0611765469e-01 3.6550728803e-01 0.0000000000e+00 0.0000e+00 -1.0000e+00
  5000001 1 8 8 0 0 +1.7762903423e-01 +3.5216623878e-01 +7.6893488344e-01 8.6996206153e-01 1.0000000000e-01 0.0000e+00 -1.0000e+00
      111 2 1 1 0 0 -1.1156454947e-01 +2.2611737964e-01 +5.5670289286e-02 2.9136660684e-01 1.3498000000e-01 0.0000e+00 0.0000e+00
       22 1 11 11 0 0 -3.2010478925e-02 +9.3599263948e-02 +3.9673254587e-02 1.0658076797e-01 0.0000000000e+00 0.0000e+00 1.0000e+00
  5000001 1 11 11 0 0 -7.9554070550e-02 +1.3251811570e-01 +1.5997034700e-02 1.8478583887e-01 1.0000000000e-01 0.0000e+00 1.0000e+00
      111 2 1 1 0 0 +2.3230845568e-01 -2.6444531472e-01 +2.6274094498e-01 4.5951164036e-01 1.3498000000e-01 0.0000e+00 0.0000e+00
       22 1 14 14 0 0 +5.9887315783e-02 -7.3536063337e-02 +3.3024333436e-02 1.0042235708e-01 0.0000000000e+00 0.0000e+00 -1.0000e+00
  5000001 1 14 14 0 0 +1.7242113990e-01 -1.9090925139e-01 +2.2971661154e-01 3.5908928328e-01 1.0000000000e-01 0.0000e+00 -1.0000e+00

I suspect that the way I generate the process is incorrect. What is the correct way of doing this?
Thanks!
Douglas