The remote server returned an error: (550) File unavailable (e.g., file not found, no access).

I get the error on the line : Dim response As FtpWebResponse = DirectCast(reqFTP.GetResponse(), FtpWebResponse)

Coding:

Private Sub Download(filePath As String, fileName As String)

        Fprogress = True
        Dim reqFTP As FtpWebRequest
        Progressinc.Value = 0
        Dim Kptotal As Double = 0
        Try
            'filePath = <<The full path where the file is to be created.>>, 
            'fileName = <<Name of the file to be created(Need not be the name of the file on FTP server).>>
            Dim outputStream As New FileStream(Convert.ToString(filePath & Convert.ToString("\")) & fileName, FileMode.Create)

            reqFTP = DirectCast(FtpWebRequest.Create(New Uri(Convert.ToString("ftp://" + ftpServerIP + "/") & fileName)), FtpWebRequest)
            reqFTP.Timeout = 1000000
            reqFTP.Method = WebRequestMethods.Ftp.DownloadFile
            reqFTP.UseBinary = True
            reqFTP.Credentials = New NetworkCredential(ftpUserID, ftpPassword)
            Dim response As FtpWebResponse = DirectCast(reqFTP.GetResponse(), FtpWebResponse)

            Dim ftpStream As Stream = response.GetResponseStream()
            Dim cl As Long = response.ContentLength
            Dim bufferSize As Integer = 4097
            Dim readCount As Integer
            Dim buffer As Byte() = New Byte(bufferSize - 1) {}

            ''Get file size 
            Dim Filesize As Long = GetFileSize(fileName)
            ''
            readCount = ftpStream.Read(buffer, 0, bufferSize)
            Progressinc.Maximum = Filesize
            Dim tempCount = 0

           While readCount > 0
                Timer1.Enabled = False
                lblStatus.Text = "."
                Application.DoEvents()
                outputStream.Write(buffer, 0, readCount)
                lblStatus.Text = ".."
                Application.DoEvents()
                Kptotal = Kptotal + readCount
                Progressinc.Value = Kptotal
                lblStatus.Text = "..."
                Application.DoEvents()
                lblPercentageInc.Text = Format(((Kptotal * 100) / Filesize), "#0.00") & " %"
                lblMB.Text = Format(Kptotal / megaByte, "#0.00") & " MB" & " / " & Format(Filesize / megaByte, "#0.00") & " MB"
                Application.DoEvents()
                lblStatus.Text = "...."
                readCount = ftpStream.Read(buffer, 0, bufferSize)
            End While
            Progressinc.Value = Progressinc.Maximum
            ftpStream.Close()
            outputStream.Close()
            response.Close()
            ''
            Timer1.Enabled = True
            lblClose_Click(Nothing, Nothing)
            Faild = 0
        Catch ex As Exception
            Faild = Faild + 1
            If DownloadErrorMessage <> ex.Message Then
                MessageBox.Show("Network Error! Update Failed!" & vbCrLf & _
                                "To stop Exe AutoUpdate!" & vbCrLf & _
                                "(" & ex.Message & ")", Me.Text, MessageBoxButtons.OK, MessageBoxIcon.Information)
            End If
            DownloadErrorMessage = ex.Message
            Progressinc.Value = 0
        End Try
    End Sub

To solve my problem Check 2 things,

 Step 1: login credentials
 Step2 : FilesName is Case Sensitive

** The problem Solved **