Commented Unassigned: UpdatePanelAnimationExtender - null reference during AsyncPostBackTrigger cast [27979]

Hi,

When I try to use UpdatePanelAnimationExtender I'm always getting the error Object reference not set to an instance of an object.
My project worked fine until I updated Ajax Control Toolkit to version 15.1.4

Thank you,
Comments: The title was edited as this issue is included in What's new list for the v16.1 release.