Exporting from SQL

Question

I am trying to export from my SQL server. I have the connection working perfectly, but I am receiving an error when I export dates/GUIDs/etc.

The error says that it is not able to cast the object from datetime to string or from uniqueidentifier to string. Is there something that I am missing here, or should I not be using string at all? I am new to C# - I am a java convert. Please be nice. If you have questions, I will do my best to answer them. Below is the code that I have thus far.

Kind Regards

         /*
         * Exports data to the CSV file.
         */

		private void exportToCSVfile(string fileOut)
		{
            // Connects to the database, and makes the select command.
            SqlConnection conn = new SqlConnection(prop.sqlConnString);
			string sqlQuery = "select * from " + this.lbxTables.SelectedItem.ToString();
			SqlCommand command = new SqlCommand(sqlQuery, conn);
			conn.Open();
			
            // Creates a SqlDataReader instance to read data from the table.
            SqlDataReader dr = command.ExecuteReader();

            // Retrives the schema of the table.
			DataTable dtSchema = dr.GetSchemaTable();

            // Creates the CSV file as a stream, using the given encoding.
			StreamWriter sw = new StreamWriter(fileOut, false, this.encodingCSV);
			
            string strRow; // represents a full row

            // Writes the column headers if the user previously asked that.
			if (this.chkFirstRowColumnNames.Checked)
			{
				sw.WriteLine(columnNames(dtSchema, this.separator));
			}

            // Reads the rows one by one from the SqlDataReader
            // transfers them to a string with the given separator character and
            // writes it to the file.
            try
            {
                while (dr.Read())
                {
                    strRow = "";
                    for (int i = 0; i < dr.FieldCount; i++)
                    {
                        strRow += dr.GetString(i);
                        if (i < dr.FieldCount - 1)
                        {
                            strRow += this.separator;
                        }
                    }
                    sw.WriteLine(strRow);
                }
            }
            catch (Exception)
            {
                MessageBox.Show("Error encountered! File creation halted.","Fatal Error!");
            }
			


            // Closes the text stream and the database connenction.
			sw.Close();
			conn.Close();

            // Notifies the user.
			MessageBox.Show("Done!");
		}