This message will appear if you are trying to open Polarbackup desktop software while you are logged into another Windows user account, not the same administrator Windows user account you were logged into it when you installed Polarbackup software on this machine in the first place.
However, even though you will not be able to open Polarbackup from this user account you are logged in to, Polarbackup will still be running and backing up your data at the scheduled time. So, when you log in to the administrator user account, you will notice that the backup did not stop.