Error while migrating 7.0 to 7.6 version

Getting below error , while running the application , what could be the issue?
Application was working fine with previous version.

Error :
[/VAADIN/widgetsets/org.vaadin.highcharts.demo.DemoWidgetSet/org.vaadin.highcharts.demo.DemoWidgetSet.nocache.js] not found from filesystem or through class loader. Add widgetset and/or theme JAR to your classpath or add files to WebContent/VAADIN folder.

Do you have a widget set named DemoWidgetSet and have you recompiled it after updating to 7.6?

yes i recompiled , and also DemoWidgetSet is from the HighCharts AddOn.

Then it sounds like it is not being included in the WAR file as it should for whatever possible reason.