There are some known issues when using both the manager and the panel in some complex applications - MasterPage or WebUserControls. However, note that a single RadAjaxManager (and no panels) in the master/main page could handle all the scenarios. Also please note that you should not add RadAjaxLoadingPanel as ajax initiator or updated control into the RadAjaxManager settings. It should be add only ad default LoadingPanel for the Manager or as LoadingPanelID to a specific Ajax setting.
All the best,
the Telerik team
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