This error occurs because the software shouldn't recommend a burning application for printing purposes. Go to Print, choose the default printer and try printing using the settings. If you have issues with the application, export the label to another format, preferably PNG or JPG, then use your favorite image viewer to print the file. However, LabelPrint is an application that is used to print the content created by it.
Additionally, check the printer for being connected and ready for printing before activating File > Print.