Java - Error al exportar Excel desde Java

Buenas,

Me salta este error al exportar Excel desde Java.

Librerias:
POI instalada 4.1.2.
Jasperreports 6.5.1

Exception in thread "AWT-EventQueue-1" java.lang.NoClassDefFoundError: org/apache/poi/hssf/util/HSSFColor$WHITE
at net.sf.jasperreports.engine.export.JRXlsExporter.<init>(JRXlsExporter.java:188)
at net.sf.jasperreports.engine.export.JRXlsExporter.<init>(JRXlsExporter.java:210)
at Form.Inf_magento.Generar_Excel(Inf_magento.java:236)
at Form.Inf_magento.btn_excelActionPerformed(Inf_magento.java:205)
at Form.Inf_magento.access$100(Inf_magento.java:45)
at Form.Inf_magento$2.actionPerformed(Inf_magento.java:109)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6539)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6304)
at java.awt.Container.processEvent(Container.java:2239)