Hello Christian Surieux,
1. Please note that you could not add control which is initially invisible on the page, to the RadAjaxManager settings. The initiator or the updated control should be always placed in a visible container so that the manager can locate it when necessary.
2. Single PageView could not be added as AJAX initiator or updated control in the AJAX settings. The only possible approach is to add the whole MultiPage in the RadAjaxManager settings or wrap the whole control into RadAjaxPanel. The other option is to locate the controls within the PageView dynamically and add the respective settings
similar to the other naming containers scenario like the WebUserControls
(see the dynamically adding settings examples there).
Let us know if further questions arise.
the Telerik team