The CLR is catching an Access Violation that’s being thrown from unmanaged code, and that is propagating up as a NullReferenceException. I’ve seen this happen with certain common control library windows types if an
application such as spy++ is running, and I see this is the TreeView control that is having troubles with a mouse down. Have you done any modification to the control through P/Invoke methods?
(from sburke_online@microsoft..nospam..com on microsoft.public.dotnet.framework.windowsforms)