That bug has been described on https://launchpad.net/distros/ubuntu/+source/nautilus/+bug/41944

"To reproduce:

Choose 'connect to server' from the Places menu
Choose Windows share and make up an IP address so it'll fail

A window opens, and an SMB icon appears on the desktop. There is a dialog box saying 'Some of the contents could not be shown'.

the window is pointless
the icon is pointless, and can't be deleted
the dialog box message is misleading: ALL contents could not be shown, and in fact the server could not be contacted at all, because it does not exist.
...
> You might want to create a bookmark for a box not running at the moment. As pointed before you can remove the icon by using the umount option from the menu. Please describe one issue by bug.
...
I'm still not entirely sure why someone would want to add a location when they have had no confirmation that it's correct. Even admins make typos!

I suggest the following:

"{...} is not a valid location. You may have made an error typing the address, or the remote computer may not currently be available.

[ ] Add this location anyway.

[OK]"

The checkbox for adding the location would be off by default, but the dialog should remember its state.
This should satisfy admins who add locations blind ;) and klutzes like me who just make mistakes
..."