If we understand the issue correctly, Lansweeper is replacing the {smartname} parameter with the machine's FQDN or NetBIOS name (as you can see when hovering over the action), but vncviewer is not accepting the parameter?
Some customers have reported this issue and were able to resolve it by using a different VNC version. The issue above is not caused by Lansweeper however, so there's nothing we can do to fix it.