From the looks of it, it seems you're having RouterOS 6.1... and you're trying to install user-manager 6.15.
It seems there's some incompatibility between the two, and so RouterOS never installs user manager. Either upgrade RouterOS to 6.15, or find user-manager 6.1.
First install 6.22 then install usermanager 6.22 your default user: admin password: "null" empty your router ip / userman : 192.168.1.1/userman maybe it helps best regards.