if (webBrowserControl.Document == null) is throwing an
InvalidCastException.

PLEASE NOTE: ***The function being called is being called from a
thread OTHER THAN than the one that created the WebBrowser
control.***  So, I think making a delegate to invoke the function from
the proper thread will solve the problem.  But, I just want to know:

Why is the above exception happening?  Where is the cast?

The StackTrace for the exception (there is no InnerException):

"   at
System.Windows.Forms.UnsafeNativeMethods.IHTMLDocument2.GetLocation()\r
\n   at System.Windows.Forms.WebBrowser.get_Document()\r\n   at MY OWN
FUNCTION... etc."

So, I guess the answer is in the above function.

Zytan