What causes the 'Cannot unregister UpdatePanel' error?

Question

I've got a UserControl that contains an UpdatePanel. When I put that on a page, it throws the following error:

Cannot unregister UpdatePanel with ID 'ReviewContentUpdatePanel' since it was not registered with the ScriptManager. This might occur if the UpdatePanel was removed from the control tree and later added again, which is not supported. Parameter name: updatePanel

ReviewContentUpdatePanel is the name of the update panel & it's not being removed or added in code, it exists in the aspx page and isn't removed. Has anyone come across this before?

Answer 1

This error occurs when the Controls collection in which the UpdatePanel is resided is cleared using the Clear method, or when the specific UpdatePanel is removed using the Remove method.

A trigger for these methods could be the implementation of the CreateChildControls method for the control contains the UpdatePanel. Usually, you call Controls.Clear() in the top of this method, to start with a clean slate if this method is called repeatedly.