How can I find error element in xml when deserialize fails?

I am trying to map a xml document to a class with xml attributes etc. When trying to deserialize and converting to my class i get error.

 return (ArticleCase)xmlSerial3c.Deserialize(xmlreader);

"There is error in xml-document (1, 3403)"

How can i locate the position (1, 3403) in the xml document? There is nothing more in exception message than this.