Vaadin Spreadsheet : implementation for com.vaadin.addon.spreadsheet.Spread

I try to install the spreadsheet demo on my project and I get this error :

Widgetset ‘com.vaadin.DefaultWidgetSet’ does not contain implementation for com.vaadin.addon.spreadsheet.Spreadsheet. Check its component connector’s @Connect mapping, widgetsets GWT module description file and re-compile your widgetset. In case you have downloaded a vaadin add-on package, you might want to refer to

My IproxWidgetSet.gwt.xml is
[font=courier new]

<?xml version="1.0" encoding="UTF-8"?> [/font]

My addon.scss is

@import “…/…/…/VAADIN/addons/spreadsheet/spreadsheet.scss”;
@mixin addons {
@include spreadsheet;

I compiled the theme and the widget set either in eclipse of with maven and some file seams to not update.

I have found my problem, my UI class did not have a @Widgetset annotation. I hope it will help someone else.