Irrlicht Engine

HI
my device is crashing, this is after showing/hiding a node many times
please check the following code, this is used to show and hide the node:

device.SceneManager.RootSceneNode.Children(k).Visible = not (device.SceneManager.RootSceneNode.Children(k).Visible)

(i am using vb.net)

any idea why is that happening?
thanks for the help

Whats the error message?

Are you sure that device.SceneManager.RootSceneNode.Children(k) is a valid SceneNode? And you aren't off by 1 on your array?