尝试打开场景构建器时如何解决此未解决的导入错误

Question

当我尝试打开场景生成器时出现此错误：

java.lang.ClassNotFoundException：未解决的导入

javafx.fxml.LoadException： /C:/Users/Mo/everett-project/src/sample/sample.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import ManufacturerPage.manuController?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.ColumnConstraints?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.layout.Pane?>
<?import javafx.scene.layout.RowConstraints?>

<GridPane alignment="center" hgap="10" vgap="10" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/8.0.121" fx:controller="sample.Controller">
    <columnConstraints>
        <ColumnConstraints />
    </columnConstraints>
    <rowConstraints>
        <RowConstraints />
    </rowConstraints>
    <children>
        <Pane prefHeight="550.0" prefWidth="765.0">
            <children>
                <Button layoutX="46.0" layoutY="103.0" mnemonicParsing="false" prefHeight="160.0" prefWidth="257.0" text="Inventory" />
                <Button layoutX="469.0" layoutY="103.0" mnemonicParsing="false" prefHeight="160.0" prefWidth="257.0" text="Transactions" />
                <Button layoutX="46.0" layoutY="330.0" mnemonicParsing="false" prefHeight="160.0" prefWidth="257.0" text="Transaction Types" />
                <Button layoutX="469.0" layoutY="330.0" mnemonicParsing="false" prefHeight="160.0" prefWidth="257.0" text="Manufacturer Information" />
                <Label layoutX="269.0" layoutY="55.0" text="Everett POS AND Inventory System" />
            </children>
        </Pane>
    </children>
</GridPane>