Are you trying to restart the nm-applet but getting a lot of errors maybe this is because nm-applet is running!
You can see all running processes with: ps -A
Or use a ‘filter’ to see applets: ps -A | grep -i applet

You may have removed the ’Notification area’ from top panel,

To put it back do the following,
- right click on top panel, “Add to Panel…”
- click on Notification Area
- Add, close