So, you have a problem with modalPanel, but not with RichFaces is general.
The Richfaces.showModalPanel() function accepts the id of the html tag, but not the id of the component. If you follow the common recommendations and use subview for included tiles, the id of the tag will not correspond to the id of the component.
For example, if you have:
<rich:modalPanel id="mypanel" .... />
the id will be "body:mypanel", but not just "mypanel". The Richfaces.showModalPanel() requires exactly the "body:mypanel". So, pay attention of the real id you have on the page.
Thanks a lot for your answer!
It works now!