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 
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 2.5.1//EN" "http://google-web-toolkit.googlecode.com/svn/tags/2.5.1/distro-source/core/src/gwt-module.dtd">
<module>
    <inherits name="com.vaadin.DefaultWidgetSet" />
    <inherits name="com.vaadin.addon.spreadsheet.Widgetset" />
</module>

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.