Question on error message "Object must implement IConvertible"

I am trying to upload the .pdf and/or .doc file to SQL Server 2000/2005. First I read the file into to the binary array byte[], then "insert into" the database. The field data type is "ntext". However, I keep getting the error: "Object must implement IConvertible". The answer in this site ( Id did search) does not address my situation. So is there anyone may offer the suggestion. BTW, I am kind of resisting the idea of using "image" field, because of the requirement.
Here are the code:


using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.IO;
using System.Data.SqlClient;
using System.Configuration;

namespace FileView
{
      /// <summary>
      /// Summary description for WebForm1.
      /// </summary>
      public class UploadImage : System.Web.UI.Page
      {
            protected System.Web.UI.WebControls.Label lblFilePath;
            protected System.Web.UI.WebControls.Button btnUpload;
            protected System.Web.UI.WebControls.RequiredFieldValidator RequiredFieldValidator1;
            protected System.Web.UI.HtmlControls.HtmlInputFile UploadFile;
            protected System.Web.UI.WebControls.TextBox txtFilePath;
      
            private void Page_Load(object sender, System.EventArgs e)
            {
                  // Put user code to initialize the page here
            }

            #region Web Form Designer generated code
            override protected void OnInit(EventArgs e)
            {
                  //
                  // CODEGEN: This call is required by the ASP.NET Web Form Designer.
                  //
                  InitializeComponent();
                  base.OnInit(e);
            }
            
            /// <summary>
            /// Required method for Designer support - do not modify
            /// the contents of this method with the code editor.
            /// </summary>
            private void InitializeComponent()
            {    
                  this.btnUpload.Click += new System.EventHandler(this.btnUpload_Click);
                  this.Load += new System.EventHandler(this.Page_Load);

            }
            #endregion

            private void btnUpload_Click(object sender, System.EventArgs e)
            {
                  if (Page.IsValid)      // Save file
                  {
                        Stream fileStream = UploadFile.PostedFile.InputStream;
                        int fileLen = UploadFile.PostedFile.ContentLength;
                        string fileType = UploadFile.PostedFile.ContentType;
                        string fileName = txtFilePath.Text;
                        byte[] fileBinaryData = new byte[fileLen];
                        int n = fileStream.Read(fileBinaryData, 0, fileLen);

                        string idis = Request.QueryString["id"];
                        int busid = System.Convert.ToInt32(idis);

                        int RowsAffected = SaveToDB(fileName, fileBinaryData, fileType, busid);
                        if (RowsAffected > 0)
                        {
                              Response.Write("<br> The File is saved.");
                        }
                        else
                        {
                              Response.Write("<br> An error occurred uploading the file");
                        }
                  }
            }

            private int SaveToDB(string fileName, byte[] fileBin, string fileContenttype, int busid)
            {
                  SqlConnection connection = new SqlConnection(ConfigurationSettings.AppSettings["DSN"]);
                  SqlCommand command = new SqlCommand("insert into LegalTemplate (DocName,  DocData, DocType, busid) values(@DocName,  @DocData, @DataType, @busid)", connection);

                  SqlParameter param0 = new SqlParameter("@DocName", SqlDbType.VarChar, 50);
                  param0.Value = fileName;
                  command.Parameters.Add(param0);

                  SqlParameter param1 = new SqlParameter("@DocData", SqlDbType.NText, 50);
                  param1.Value = fileBin;
                  command.Parameters.Add(param1);

                  SqlParameter param2 = new SqlParameter("@DataType", SqlDbType.VarChar, 50);
                  param2.Value = fileContenttype;
                  command.Parameters.Add(param2);

                  SqlParameter param3 = new SqlParameter("@busid", SqlDbType.Int, 4);
                  param3.Value = busid;
                  command.Parameters.Add(param3);

                  connection.Open();
                  int numRowsAffected = command.ExecuteNonQuery();  // the error is right here.!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! The issue is related to the DocData (ntext0 field. If you remove DocData from the command, it works fine.
                  connection.Close();

                  return numRowsAffected;
            }
      }
}