public static void validatexml(String str)
        {
            XmlValidatingReader validate= null;
            //URL of path containing XML data
            XmlTextReader xRead = new XmlTextReader(str); //Load selected document
            validate = new XmlValidatingReader(xRead); //Validate xmlreader
            validate.ValidationType = ValidationType.Schema; //Validate Schema of loaded xml file
            validate.ValidationEventHandler += new ValidationEventHandler(ValidationCallBack);

            try
            {
                while (validate.Read())
                { }
                if (m_valid)
                {
                    MessageBox.Show("Valid documnent");
                    m_valid = true;
                }
            }
            catch
            {
                MessageBox.Show("Incorrect file or XML document not well formed");
            }
            
            validate.Close();
        }

 public static void ValidationCallBack(object sender,ValidationEventArgs args)
        {
            MessageBox.Show("Validation error :" + args.Message);
            m_valid = false;
        }