This error message indicates that your email configuration settings for the form are incomplete.
Please go to the administration panel of your website, navigate to Components -> Visforms and open the form in question in the edit view.
Click the tab "Mail Options"
Make sure the following three Options contain a valid email address each.
- For the "Options for result mail" the option "Mail From Address"
- For the "Options for result mail" option "Mail To"
- For the "Options for recipient mail" the Option "Mail From Address"