File upload using Threading - vb.net

Question

I have written a code to upload a file using thread.I have place a simple file upload control and a button on a page.The code looks like this-
Protected Sub btnUpload_Click(ByVal sender As Object,
ByVal e As EventArgs) Handles btnUpload.Click
Dim timeStart As TimeSpan = Nothing
Dim timeEnd As TimeSpan = Nothing
Dim timeDiff As TimeSpan = Nothing
Dim ex As Exception = Nothing
Dim FileNameWithoutExtension As String = String.Empty
Try
Dim objTh As Thread = Nothing
objTh = New Thread(AddressOf SaveFileByBuffering)
timeStart = DateTime.Now.TimeOfDay
objTh.IsBackground = True
FileNameWithoutExtension = System.IO.Path.GetFileName(FldUploadThreading.FileName)
objTh.Start("New_" + FileNameWithoutExtension)
objTh.Name = "ARAThreadFileBuffer"
objTh.Join()
timeEnd = DateTime.Now.TimeOfDay
timeDiff = timeEnd - timeStart
Catch exThAbort As ThreadAbortException
ex = exThAbort
Catch exTh As ThreadStartException
ex = exTh
Catch exCommon As Exception
ex = exCommon
End Try
End Sub
the method to be called using thread:
Public Function SaveFileByBuffering(ByVal lstrFilePath As String)
Dim bufferSize As Integer = 512
Dim buffer As Byte() = New Byte(bufferSize - 1) {}
Dim pathUrl As String = ConfigurationManager.AppSettings("strFilePath").ToString()
Dim uploadObj As UploadDetail = New UploadDetail()
uploadObj.IsReady = True
uploadObj.FileName = lstrFilePath
uploadObj.ContentLength = Me.FldUploadThreading.PostedFile.ContentLength
Me.Session("UploadXDetail") = uploadObj
Dim Upload As UploadDetail = DirectCast(Me.Session("UploadXDetail"), UploadDetail)
Dim fileName As String = Path.GetFileName(Me.FldUploadThreading.PostedFile.FileName)
Using fs As New FileStream(Path.Combine(pathUrl, lstrFilePath), FileMode.Create)
While Upload.UploadedLength < Upload.ContentLength
Dim bytes As Integer = Me.FldUploadThreading.PostedFile.InputStream.Read(buffer, 0, bufferSize)
fs.Write(buffer, 0, bytes)
Upload.UploadedLength += bytes
End While
End Using
End Function
There are two issues:
When some one clicks on the same button simultaneously the thread behavior works in a different way , some time page crashes.
When this process i have tested on multiuser environment with 60 users and file size is 25 MB each user the page crashed.
I have .net 3.5 so i have no choice with advance version of file upload in 2010 or later version.