550 error

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C#

ASP.NET

I am using C# .net code for sending mail with attachments.

mail has been successfully send but when i try to delete that attachment from the web folder the error is 550! the file is used by another process.

can you help me what should i do.
::code::

MailMessage mail;
SmtpClient objsmtp;

try
{
string FileName = Server.MapPath("~//EmailTemp.htm");
string FileContents;
System.IO.StreamReader myStreamReader;

if ((FileName != null))
{
myStreamReader = System.IO.File.OpenText(FileName);
FileContents = myStreamReader.ReadToEnd();
FileContents = FileContents.Replace("%Name%", tbxName.Text);
FileContents = FileContents.Replace("%Email%", tbxEmail.Text);
FileContents = FileContents.Replace("%Country%", tbxCountry.Text);
FileContents = FileContents.Replace("%Patients Testimonials%", tbxPatTestimonials.Text);



mail = new MailMessage();
String email = "email@yahoo.in";
mail.To.Add(tbxEmail.Text);
mail.Bcc.Add(email);
mail.From = new MailAddress("email@domainname.com");
string attach1 = null;

string strFileName = null;
if (fudReports .FileName != null)
{
// Get a reference to PostedFile object

// Get the file name
strFileName = Path.GetFileName(fudReports.FileName);
// Preced the file name with "attachments/" so
// the file is saved to our attachments directory
strFileName = "attachments/" + strFileName;
// Save the file on the server
fudReports.SaveAs(Server.MapPath(strFileName));
// Create the email attachment with the uploaded file
Attachment attach = new Attachment(Server.MapPath(strFileName));

// Attach the newly created email attachment
mail.Attachments.Add(attach);
// Store filename so we can delete it later
attach1 = strFileName;

}





mail.Subject = "Enquiry Mail";
mail.Body = FileContents.ToString();


mail.Priority = MailPriority.High;
mail.IsBodyHtml = true;
objsmtp = new SmtpClient();


objsmtp.Host = "hoshing server name";
objsmtp.UseDefaultCredentials = true;

objsmtp.Credentials = new System.Net.NetworkCredential("email@domianname.com", "Password");
objsmtp.DeliveryMethod = SmtpDeliveryMethod.Network;


objsmtp.Send(mail);
myStreamReader.Dispose();
FileName = null;

FileContents = null;
if (attach1 != null)
File.Delete(Server.MapPath(strFileName));

attach1 = null;

}
}
catch (Exception ex)
{
//divMess.InnerText = ex.Message;
}
finally
{
mail = null;
objsmtp = null;


}