Web services access problem

[Farm]

I have written a generic proxy class for web services access
This proxy class runs in the web server
The class works fine if the browser runs in LAN, however it generates the following error if i access from remote machine

-----------------------------------------------------------------------------------------------------
Object reference not set to an instance of an object.

Description
An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details
System.NullReferenceException: Object reference not set to an instance of an object

Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace
[NullReferenceException: Object reference not set to an instance of an object.]
Farm.Web.Controls.SoapMethod.ServerExecute(String SoapHost, String SoapServer, String SoapNameSpace, HttpRequest Request, HttpSessionState Session) in SoapMethod.vb:25
Farm.Web.Controls.ComboBox.Render(HtmlTextWriter output) in ComboBox.vb:426
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +243
System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +72
System.Web.UI.Control.Render(HtmlTextWriter writer) +7
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +243
System.Web.UI.Page.ProcessRequestMain() +192
-----------------------------------------------------------------------------------------------------

Some server code

With HTTPRe

.Proxy = GlobalProxySelection.GetEmptyWebProxy()

.ContentType = "text/xml; charset=utf-8
.Method = "POST
.KeepAlive = Fals

.Credentials = CredentialCache.DefaultCredential

Dim i As Int3

Dim strKey As Strin

For i = 0 To Request.Headers.Count -
strKey = Request.Headers.GetKey(i
AddHeader(strKey, Request.Headers(strKey)) 'utility functio
Nex

.CookieContainer = New CookieContaine
.CookieContainer.GetCookies(curUri) 'get the list of cookies to send to the destination site

Dim app As New CookieCollectio

For i = 0 To Request.Cookies.Count -
app.Add(CastCookie(Request.Cookies.Item(i), Request.ServerVariables("HTTP_HOST"))
Nex

.CookieContainer.Add(app

End Wit

Dim strm As System.IO.StreamWrite
Dim XML As New System.Xml.XmlDocumen
Dim HttpRes As HttpWebRespons

Tr
'Write the Request Strea
error here------> strm = New StreamWriter(HTTPReq.GetRequestStream(), Encoding.UTF8
........