The DataContext type cannot be determined because the Type property specified in the DesignData binding either cannot be ...

The DataContext type cannot be determined because the Type property specified in the DesignData binding either cannot be found or is not specified. When using design-time data in JSON format, the Type property must be specified for the schema to be determined.

If the Type property has already been specified, close the dialog box by clicking OK, and then build your project.

To set a custom path, select Custom.