a4j:include is similar to jsp:include or ui:include
If you use facelets it should be .xhtml . Otherwise, it should .jsp (or jspx or whatever you use)
So, what the exception you have got?
Sorry, that was my fault. I didn't use f:subview in my include-file.
Everything works fine so far, but how could I use returns in the rich:tab? If I use the brake-return will be made outsite the tab(Panel) (I dont't want to use the -tag)
As usual for JSF, the plain html in not allowed without f:verbatim. Only facelets or JSF 1.2 allows it