roslaunch command producing RLException

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I accidently delete ROS from my Ubuntu 18. After reinstalling, Im trying to use roslaunch command and execute a .launch file from a known package - which worked perfectley untill i reinstalled ROS. Can anyone please point out something that might be a problem, or a solution?

user@User:~/catkin_ws$ roslaunch pkg_name launch_name.launch
RLException: [launch_name.launch] is neither a launch file in package [pkg_name] nor is [pkg_name] a launch file name
The traceback for the exception was written to the log file