XSLT compile error.

Thank you Fouad, that's very helpful. I need to output at least two styles to be viewed in a browser.

I am getting another error now:

The program isn't writing to my xml file. Any idea where I am going wrong? Thanks in advance for your help. Here is my code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Data.OleDb;
using System.Xml;
using System.Xml.Xsl;
using System.Xml.XPath;

namespace CSVImporter
{

    public partial class CSVImporter : Form
    {
        //const string xmlfilename = @"C:\Users\fenwky\XmlDoc.xml"; - file name and location of xml file
        const string xmlfilename = @"C:\Users\fenwky\XmlDoc.xml";

        // New code
        //const string xmlfilename = @"C:\Users\fenwky\XmlDoc.xml"; - file name and location of xsl file
        const string stylesheetsimple = @"C:\Users\fenwky\style1.xsl";


        //const string xmlfilecomplex = @"C:\Users\fenwky\XmlDoc2.xml";
        const string xmlfilecomplex = @"C:\Users\fenwky\XmlDoc2.xml";

        DataSet ds = null;


        public CSVImporter()
        {
            InitializeComponent();
            // Create a Open File Dialog Object.
            openFileDialog1.Filter = "csv files (*.csv)|*.csv|All files (*.*)|*.*";
            openFileDialog1.ShowDialog();
            string fileName = openFileDialog1.FileName;


            //doc.InsertBefore(xDeclare, root);
            // Create a CSV Reader object.
            CSVReader reader = new CSVReader();
            ds = reader.ReadCSVFile(fileName, true);
            dataGridView1.DataSource = ds.Tables["Table1"];

        }

        private void WXML_Click(object sender, EventArgs e)
        {
            WriteXML();
        }

        public void WriteXML()
        {

            StringWriter stringWriter = new StringWriter();
            ds.WriteXml(new XmlTextWriter(stringWriter), XmlWriteMode.WriteSchema);
            string xmlStr = stringWriter.ToString();
            XmlDocument doc = new XmlDocument();
            doc.LoadXml(xmlStr);
            XmlDeclaration xDeclare = doc.CreateXmlDeclaration("1.0", "UTF-8", null);
            XmlNode docNode = doc.CreateXmlDeclaration("1.0", "UTF-8", null);

            doc.InsertBefore(xDeclare, doc.FirstChild);

            // Load the style sheet.
            XslCompiledTransform xslt = new XslCompiledTransform();
            xslt.Load("style1.xsl");

            // Transform the file and output an HTML string. 
            string HTMLoutput;
            StringWriter writer = new StringWriter();
            xslt.Transform("XmlDoc.xml", null, writer);
            HTMLoutput = writer.ToString();
            writer.Close();

            var piText = "type=\"text/xsl\" href=\"style1.xsl\"";
            var newPI = doc.CreateProcessingInstruction("xml-stylesheet", piText);
            doc.InsertAfter(newPI, doc.FirstChild);

            // Save document
            doc.Save(xmlfilename);

        }

        private void btExportComplexXML_Click(object sender, EventArgs e)
        {
            WriteXMLComplex();
        }

        public void WriteXMLComplex()
        {
            // Creates stringwriter
            StringWriter stringWriter = new StringWriter();
            ds.WriteXml(new XmlTextWriter(stringWriter), XmlWriteMode.WriteSchema);

            string xmlStr = stringWriter.ToString();

            XmlDocument doc = new XmlDocument();
            doc.LoadXml(xmlStr);

            XmlDeclaration xDeclare = doc.CreateXmlDeclaration("1.0", "UTF-8", null);
            XmlNode docNode = doc.CreateXmlDeclaration("1.0", "UTF-8", null);

            doc.InsertBefore(xDeclare, doc.FirstChild);

            // Create a procesing instruction.
            // XmlProcessingInstruction newPI;
            // Uses XML transformation.
            // String PItext = "<abc:stylesheet xmlns:abc=\"http://ift.tt/1N6W08z; version=\"1.0\">";
            // newPI = doc.CreateProcessingInstruction("xsl:stylesheet", PItext);
            // doc.InsertAfter(newPI, doc.FirstChild);

            // Try this code as 
            var piText = "type=\"text/xsl\" href=\"style1.xsl\"";
            var newPI = doc.CreateProcessingInstruction("xml-stylesheet", piText);
            doc.InsertAfter(newPI, doc.FirstChild);

            // Saves document.
            doc.Save(xmlfilecomplex);

        }
    }

    //Creates a CSVReader Class
    public class CSVReader
    {

        public DataSet ReadCSVFile(string fullPath, bool headerRow)
        {

            string path = fullPath.Substring(0, fullPath.LastIndexOf("\\") + 1);
            string filename = fullPath.Substring(fullPath.LastIndexOf("\\") + 1);
            DataSet ds = new DataSet();

            try
            {
                if (File.Exists(fullPath))
                {
                    string ConStr = string.Format("Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0}" + ";Extended Properties=\"Text;HDR={1};FMT=Delimited\\\"", path, headerRow ? "Yes" : "No");
                    string SQL = string.Format("SELECT * FROM {0}", filename);
                    OleDbDataAdapter adapter = new OleDbDataAdapter(SQL, ConStr);
                    adapter.Fill(ds, "TextFile");
                    ds.Tables[0].TableName = "Table1";
                }
                foreach (DataColumn col in ds.Tables["Table1"].Columns)
                {
                    col.ColumnName = col.ColumnName.Replace(" ", "_");
                }
            }

            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            return ds;
        }
    }
}