Hi, we're trying to use the ASP.NET AJAX controls in our SharePoint pages as visual web parts. We've only used the RadGrid, RadComboBox & RadAjaxManager and they seem to work for the most part. We're trying to incorporate the RadScriptManager as well. We can't add it inside the web part as SharePoint throws the error "Only one instance of a ScriptManager can be added to the page". Which makes sense as the MasterPage (seattle.master) uses a ScriptManager. So, we've tried removing the ScriptManager and replace it with RadScriptManager like:
The <!--SPM:--> tag is used in the seattle.html because MS don't recommend you edit the seattle.master file directly in SharePoint 2013. But it throws the same error "Only one instance of a ScriptManager can be added to the page" in the ULS logs. It's like SharePoint is ignoring the RadScriptManager control.
We're using version 2018.1.117.40 of the ASP.NET AJAX controls and SharePoint 2013 (15.0.4569.1000) with the latest patches as at 2018/02/16.