I think you need to debug the web method code to see where you are
generating the null reference exception.  

I hope this helps

Dan Rogers
Microsoft Corporation
--------------------
From: ksubha@gmail.com (subha)
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Subject: Webservice works on the browser but not from C# app
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I have a HelloWorld webservice that works on my IE browser. But, when
I add a webreference to it and call the HelloWorld method from my
WindowsFormsApp (return in C#), I get error messages. The error
messages differ depending on when I restart my machine.

RIGHT AFTER RESTART:

'WindowsApplication1.exe': Loaded 'oevrvyg9', No symbols loaded.
A first chance exception of type 'System.NullReferenceException'
occurred in system.dll

Additional information: Object reference not set to an instance of an
object.

A first chance exception of type 'System.Net.Sockets.SocketException'
occurred in system.dll

Additional information: An established connection was aborted by the
software in your host machine

A first chance exception of type 'System.IO.IOException' occurred in
system.dll

Additional information: Unable to read data from the transport
connection.

A first chance exception of type 'System.Net.WebException' occurred in
system.dll

Additional information: The underlying connection was closed: An
unexpected error occurred on a receive.

A first chance exception of type 'System.Net.WebException' occurred in
system.web.services.dll

Additional information: The underlying connection was closed: An
unexpected error occurred on a receive.

  at
System.Web.Services.Protocols.WebClientProtocol.GetWebResponse(WebRequest
request)
  at
System.Web.Services.Protocols.HttpWebClientProtocol.GetWebResponse(WebReques
t
request)
  at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String
methodName, Object[] parameters)
  at WindowsApplication1.localhost.Service1.HelloWorld() in
D:\WindowsApplication1\Web References\localhost\Reference.cs:line 37
  at WindowsApplication1.Form1.cmdBegin_Click(Object sender,
EventArgs e) in d:\windowsapplication1\form1.cs:line 97

SECOND TIME:

Additional information: The operation has timed-out.

A first chance exception of type 'System.Net.WebException' occurred in
system.dll

Additional information: The operation has timed-out.

A first chance exception of type 'System.Net.WebException' occurred in
system.web.services.dll

Additional information: The operation has timed-out.

  at
System.Web.Services.Protocols.WebClientProtocol.GetWebResponse(WebRequest
request)
  at
System.Web.Services.Protocols.HttpWebClientProtocol.GetWebResponse(WebReques
t
request)
  at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String
methodName, Object[] parameters)
  at WindowsApplication1.localhost.Service1.HelloWorld() in
D:\WindowsApplication1\Web References\localhost\Reference.cs:line 37
  at WindowsApplication1.Form1.cmdBegin_Click(Object sender,
EventArgs e) in d:\windowsapplication1\form1.cs:line 97