Created Unassigned: Element 'ScriptManager' is not a known element [27908]

Hi,
I updated the AjaxControlToolKit, but now I have this Issue.

in my web Config I have this:
<pages>
<controls>
<add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" />
</controls>
</pages>

I Used Nuget, I need to do someting else?