Error when matching ttw to ttwj

Hi,

I met a problem when trying to match ttw with ttwj. The code I used is,

>define p = p b b~
>generate p p > t t~ w+ @1
>add process p p > t t~ w+ j @2

and then MG5 said

 P2_qq_ttxwpg SubProcesses doesn't have available phase-space.
            Please check mass spectrum.
INFO: Idle: 0, Running: 5, Completed: 1 [ current time: 19h22 ]
INFO: Idle: 0, Running: 4, Completed: 2 [ 0.073s ]
INFO: Idle: 0, Running: 0, Completed: 6 [ 0.9s ]
INFO: End survey
refine 10000
Creating Jobs
INFO: Refine results to 10000
INFO: Generating 10000.0 unweigthed events.
Error when reading /home/kpxie/MG5_aMC_v2_6_3_2/SM_test2/SubProcesses/P2_gq_ttxwpq/G1/results.dat
Command "generate_events run_01" interrupted with error:
IOError : [Errno 2] No such file or directory: '/home/kpxie/MG5_aMC_v2_6_3_2/SM_test2/SubProcesses/P2_gq_ttxwpq/G1/results.dat'
Please report this bug on https://bugs.launchpad.net/mg5amcnlo
More information is found in '/home/kpxie/MG5_aMC_v2_6_3_2/SM_test2/run_01_tag_1_debug.log'.
Please attach this file to your report.

I don't know why it reported 'P2_qq_ttxwpg SubProcesses doesn't have available phase-space', because the 13 TeV collision energy is able to produce t t~ w+ g. And I checked that

>generate p p > t t~ w+

>generate p p > t t~ w+ j

both work well separately. I don't know why errors occur when combining the two codes together. Would you please help me? Thank you!

Best,
Ke-Pan Xie