Hi Mandeep,
Mendix is trying to kill a session for the user, however it seems that the user is running a long action. Is it possible to see what kind of action this is in the 'running now' section?
This action might be for example an infinite loop?
Check out this forum post: https://forum.mendix.com/link/questions/86481 it is kind of the same issue.
If you stop and restart the application the session will be killed and you could porbably acces the application again.