Problem to retrieve image

Hi,
I am to retrieve one picture file from an Access table, using these

                OleDbCommand cmd = new OleDbCommand("SELECT [photo_file] FROM [ite_tab3] where [ite_id]=@par_id", conn);
                if (tb_iteabbr.Text!="")
                {
                    cmd.Parameters.Add("@par_id", OleDbType.VarChar).Value = lb_iteid.Text.Trim();
                }
                else
                {
                    cmd.Parameters.Add("@par_id", OleDbType.VarChar).Value = "";
                }
                byte[] bArray = (byte[])cmd.ExecuteScalar();
                MemoryStream fs = new MemoryStream(bArray);
                System.Drawing.Image img = new System.Drawing.Bitmap(fs);
                using (FileStream fw = new FileStream(Path.Combine(Server.MapPath("~/"), "output" + Session["counter"].ToString() + ".jpg"), FileMode.Create))
                {
                    fw.Write(bArray, 0, bArray.Length);
                }

                fs.Flush();
                fs.Close();
                ...

but I get this exception error. how to adjust the above codes?
Server Error in '/App18_devst' Application.

Buffer cannot be null.
Parameter name: buffer
  Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

 Exception Details: System.ArgumentNullException: Buffer cannot be null.
Parameter name: buffer

Source Error:


 An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  

Stack Trace:



[ArgumentNullException: Buffer cannot be null.
Parameter name: buffer]
   System.IO.MemoryStream..ctor(Byte[] buffer, Boolean writable) +14257217
   App18._Default.refresh_img() +438
   App18._Default.BindData() +442
   App18._Default.refresh_pg() +10636
   App18._Default.Page_Load(Object sender, EventArgs e) +724
   System.Web.UI.Control.LoadRecursive() +71
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3178

 


Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.18408 

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Many Thanks & Best Regards, Hua Min