I beleive you have to read the entire file in order for it to validate try this

Settings = new XmlReaderSettings();
Settings.ValidationType = ValidationType.Schema;
Settings.Schemas.Add("http://tempuri.org/Unit.xsd", Directory.GetCurrentDirectory() + strXmlSchema);
Settings.ValidationEventHandler += new ValidationEventHandler(OnSchemaValidationError);

using (XmlReader Reader = XmlReader.Create(Directory.GetCurrentDirectory() + strXmlFile, Settings))
{
if (Reader != null)
{
while(Reader.Read()){}
}
}

Don't know if they like product recommendations here but this is what I have used in the past http://www.jollans.com/tiki/tiki-index.php

I'm assuming your using autoscroll I have had better luck setting the postion

int distX += HorizontalScroll.Value;
int distY += VerticalScroll.Value;
//do some sort of range check
//then set the AutoScrollPostion
AutoScrollPosition = new Point(x, y);

hope this helps