Script Task Error --Object reference not set to an instance of an object

I am trying to execute this code feom Script task while excuting its giving me error that "Object reference not set to an instance of an object." The assemblies Iam referening in this code are there in GAC. Any idea abt this.

Thanks,

PublicSub Main()

Dim remoteUri AsString

Dim fireAgain AsBoolean

Dim uriVarName AsString

Dim fileVarName AsString

Dim httpConnection As Microsoft.SqlServer.Dts.Runtime.HttpClientConnection

Dim emptyBytes(0) AsByte

Dim SessionID AsString

Dim CusAuth As CustomAuth

Try

' Determine the correct variables to read for URI and filename

uriVarName = "vsReportUri"

fileVarName = "vsReportDownloadFilename"

' create SessionID for use with HD Custom authentication

CusAuth = New CustomAuth(ASCIIEncoding.ASCII.GetBytes(Dts.Variables("in_vsBatchKey").Value.ToString()))

Dts.Variables(uriVarName).Value = Dts.Variables(uriVarName).Value.ToString() + "&" + _

"BeginDate=" + Dts.Variables("in_vsBeginDate").Value.ToString() + "&" + _

"EndDate=" + Dts.Variables("in_vsEndDate").Value.ToString()

Dim request As HttpWebRequest = CType(WebRequest.Create(Dts.Variables(uriVarName).Value.ToString()), HttpWebRequest)

'Set credentials based on the credentials found in the variables

request.Credentials = New NetworkCredential(Dts.Variables("in_vsReportUsername").Value.ToString(), _

Dts.Variables("in_vsReportPassword").Value.ToString(), _

Dts.Variables("in_vsReportDomain").Value.ToString())

'Place the custom authentication session ID in a cookie called BatchSession

request.CookieContainer.Add(New Cookie("BatchSession", CusAuth.GenerateSession("EmailAlertingSSIS"), "/", Dts.Variables("in_vsReportDomain").Value.ToString()))

' Set some reasonable limits on resources used by this request

request.MaximumAutomaticRedirections = 4

request.MaximumResponseHeadersLength = 4

' Prepare to download, write messages indicating download start

Dts.Events.FireInformation(0, String.Empty, String.Format("Downloading '{0}' from '{1}'", _

Dts.Variables(fileVarName).Value.ToString(), Dts.Variables(uriVarName).Value.ToString()), String.Empty, 0, fireAgain)

Dts.Log(String.Format("Downloading '{0}' from '{1}'", Dts.Variables(fileVarName).Value.ToString(), Dts.Variables(uriVarName).Value.ToString()), 0, emptyBytes)

' Download data

Dim response As HttpWebResponse = CType(request.GetResponse(), HttpWebResponse)

' Get the stream associated with the response.

Dim receiveStream As Stream = response.GetResponseStream()

' Pipes the stream to a higher level stream reader with the required encoding format.

Dim readStream AsNew StreamReader(receiveStream, Encoding.UTF8)

Dim fileStream AsNew StreamWriter(Dts.Variables(fileVarName).Value.ToString())

fileStream.Write(readStream.ReadToEnd())

fileStream.Flush()

fileStream.Close()

readStream.Close()

fileStream.Dispose()

readStream.Dispose()

'Download the file and report success

Dts.TaskResult = Dts.Results.Success

Catch ex As Exception

' post the error message we got back.

Dts.Events.FireError(0, String.Empty, ex.Message, String.Empty, 0)

Dts.TaskResult = Dts.Results.Failure

EndTry

EndSub

It isn't clear what is failing, a line number or similar would help. Since you mention external assemblies, have you read this -

Referencing Other Assemblies in Scripting Solutions
(http://msdn2.microsoft.com/en-us/library/9b655bcd-19f6-43d8-9f89-1b4d299c6380.aspx)