Can't integrate add-on after install and uninstall Liferay IDE for Eclipse

With my eclipse environment, I was able to use add-on before.

Recently I developed couple liferay portlets using vaadin and I installed liferay IDE for Eclipse. My understanding is that liferay manage its widgetsets separately.

After finished the Liferay development, I went back to my other vaadin project and found that I can’t integrate with add-ons any more. I will get the jar file and put it in the web-INF/lib directory and the eclipse will automatically compile and add-on. But the application kept saying "widgetset does not contain implementation… ".

I thought the liferay IDE for eclipse might be interfering with it and then unistall the plug in.

But I still get the same error. What do I need to do?

I can see that the “widgetsets” directory under webContent is compiled and seems to have the add-on. But why the application can’t find the implementation? Where should I check next?

Thanks a bunch.