If you get the "Can't start root mode Krusader, because kdesu is missing from the path" when you try to invoke the "Start Root Mode Krusader" option here is what you need to do.
Go to settings, configure krusader.
Select Dependencies tab and put /usr/bin/kdesudo in the kdesu field. Click apply.
Select 'Start Root Mode Krusader' from the tools menu.
Now you get the correct password prompt and you are set.
