I use Infragistics' (used to be ProtoView) DataExplorer which is an ActiveX control similar to the MS TreeView control. I have seen Dr. Watson only when I've programmed very badly. Things like pointing to nodes that don't exist, or referencing some property that has not yet been initialized.

I suggest stepping through your code and trying to pinpoint where it's happening.

Perhaps you can insert the treeview-loading code into a regular form and see if that changes things or helps you debug.