That message occurs when the .wie file has widgets that are not registered by your theme or a plugin. Make sure the theme and any plugins it requires are installed and active. The provider of your .wie file and theme may be able to help you with this.
Are you still having trouble with this?
Made several attempts to import agent-focused-sample-widgets.wie and get the error message ‘You must upload a .wie file generated by this plugin’. I’m not able to utilize the StudioPress Demo Widgets for the Demo Agent Focused Demo Theme.
@dragiron103 Please open a support thread of your own and share which version of the plugin and WordPress you are using. Thank you.
Closing original thread due to inactivity, assuming resolved (@lauratoldy, feel free to reply if you are still having an issue).