I am using a component (GoogleMapControl) that inherit IExtenderControl . when i add it in to radajaxmanager updated controls or if i use it in dynamically loaded usercontrol by RadTab & RadMultiPage i am getting error of Unable to cast object of type 'GoogleMaps.Markers.GoogleMarkers' to type 'System.Web.UI.ExtenderControl'.

When i check the error detail by AsyncPostBackError event, i found that error comes from Telerik.Web.UI.ProxyScriptControl.GetChildScriptDescriptorsRecursive(Control parent, ArrayList scriptDescriptors).

Someones lived same problem old but same... As in https://dnntracker.atlassian.net/browse/DNN-25819