Error: can not launch node of type

[bkhnk48]

I install arena-rosnav by following the guide:
https://arena-rosnav.readthedocs.io/en/latest/user_guides/installation/
And as I run the statement:
roslaunch arena_bringup start_training.launch
I always get the error:
process[eval_sim/transform_broadcaster-9]: started with pid [176353]

ERROR: cannot launch node of type [flatland_server/flatland_server]: Cannot locate node of type [flatland_server] in package [flatland_server]. Make sure file exists in package path and permission is set to executable (chmod +x)
ERROR: cannot launch node of type [pedsim_simulator/pedsim_simulator]: Cannot locate node of type [pedsim_simulator] in package [pedsim_simulator]. Make sure file exists in package path and permission is set to executable (chmod +x)

How could I fix this problem?
Thank you in advance

[tuananhroman]

Have you already tried to source the environment setup file? Also, you need to specify the arguments of the launch file.