Amazon S3: A WebException with status SendFailure was thrown - vb.NET

Question

I have been developing a service that will upload/download files to and from the AWS S3 Cloud Service. The following code runs fine, but I'm getting the error "Web exception with status Send failure was thrown" or "The underlying connection was closed: An unexpected error occurred on a send" more often than not. Please find below the list of links I checked. None of them seem to solve the issue. Any help would be appreciated.

Links I checked:

1. https://blogs.msdn.microsoft.com/jpsanders/2009/01/07/you-receive-one-or-more-error-messages-when-you-try-to-make-an-http-request-in-an-application-that-is-built-on-the-net-framework-2-0/
2. C# HttpWebRequest The underlying connection was closed: An unexpected error occurred on a send
3. https://forums.asp.net/t/2037197.aspx?C+HttpWebRequest+The+underlying+connection+was+closed+An+unexpected+error+occurred+on+a+send+

---

Code to Upload:

Private Shared Function Upload(ByVal S3Key As String, ByVal bucketName As String, ByRef client As IAmazonS3, ByVal filePath As String) As String
        Try
            Dim putRequest As New PutObjectRequest
            putRequest.BucketName = bucketName
            putRequest.Key = S3Key
            putRequest.FilePath = filePath
            putRequest.Metadata.Add("x-amz-meta-title", "someTitle")
            putRequest.Metadata.Add("Entity", "entity")
            putRequest.Metadata.Add("DocumentType", "docType")
            putRequest.Metadata.Add("UploadDate", DateTime.UtcNow.ToShortDateString())
            putRequest.Metadata.Add("Content-Type", "contentType")

            Dim response As PutObjectResponse = client.PutObject(putRequest)

        Catch amazonS3Exception As AmazonS3Exception
            If amazonS3Exception.ErrorCode IsNot Nothing AndAlso (amazonS3Exception.ErrorCode.Equals("InvalidAccessKeyId") OrElse amazonS3Exception.ErrorCode.Equals("InvalidSecurity")) Then
                Return "Invalid AWS Credentials"
            Else
                Return "Error occurred. Message:'{0}' when writing an object" + amazonS3Exception.Message
            End If
        End Try
    End Function

---

Code to Download:

Public Function AWSFileDownload(ByVal fname As String, ByVal strFileType As Int32) As String
        Try
            Dim path As Path
            Dim data As String
            Dim awsAccessKey = System.Configuration.ConfigurationManager.AppSettings("AWSACCESSKEY")
            Dim awsSecretKey = System.Configuration.ConfigurationManager.AppSettings("AWSSECRETKEY")
            Dim bucketName_Documents = System.Configuration.ConfigurationManager.AppSettings("bucketName_Documents")
            Dim bucketName_OtherDocuments = System.Configuration.ConfigurationManager.AppSettings("bucketName_OtherDocuments")
            Dim S3Key As String = fname
            Dim type As String = ""
            Dim dest As String = ""
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
            Using s3Client = New AmazonS3Client(awsAccessKey, awsSecretKey, RegionEndpoint.USEast1)

                Dim request As New GetObjectRequest()
                If (strFileType = "0") Then
                    request.BucketName = bucketName_OtherDocuments
                ElseIf (strFileType = "1") Then
                    request.BucketName = bucketName_Documents
                End If
                request.Key = S3Key
                Using response As GetObjectResponse = s3Client.GetObject(request)
                    Dim ext = Path.GetExtension(S3Key)
                    If Not IsDBNull(ext) Then
                        ext = LCase(ext)
                    End If
                    Select Case ext
                        Case ".htm", ".html"
                            type = "text/HTML"
                        Case ".txt"
                            type = "text/plain"
                        Case ".doc", ".rtf"
                            type = "Application/msword"
                        Case ".csv", ".xls"
                            type = "Application/x-msexcel"
                        Case ".docx"
                            type = "Application/vnd.openxmlformats-officedocument.wordprocessingml.document"
                        Case ".xlsx"
                            type = "Application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
                        Case Else
                            type = "text/plain"
                    End Select
                    dest = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), S3Key)
                    If Not File.Exists(dest) Then
                        response.WriteResponseStreamToFile(dest)
                    End If
                End Using
            End Using
            Response.ClearHeaders()
            Response.AppendHeader("content-disposition", "attachment; filename=" + S3Key)
            If type <> "" Then
                Response.ContentType = type
            End If
            Response.WriteFile(dest)
            Response.End()
        Catch amazonS3Exception As AmazonS3Exception
            If amazonS3Exception.ErrorCode IsNot Nothing AndAlso (amazonS3Exception.ErrorCode.Equals("InvalidAccessKeyId") OrElse amazonS3Exception.ErrorCode.Equals("InvalidSecurity")) Then
                Return "Invalid AWS Credentials"
            Else
                Return "Error occurred. Message:'{0}' when writing an object" + amazonS3Exception.Message
            End If
        End Try
    End Function