Yee-Ha !
Have been having problems with C5 exception errors in a few of our installations for about the past six months.
Finally figured out today that turning Norton's Anti-virus 2001's "script locking" option eliminated these errors. This option was killing the app upon calls to DBI treeview, toolbar controls.
MS has recently been made aware of this problem and will be updating MSDN with it shortly.
Thanks to all of you who helped address this issue.
Puritanism - The secret fear that someone, somewhere is having fun.