We have a web service that's been returning a SoapException stating that 'Object reference not set to an instance of an object.'. Unfortunately, it's only doing it in one particular environment.  We set up a SoapExtension to trace the messages, ala information at this article (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cp
conalteringsoapmessageusingsoapextensions.asp) at MSDN.  That article shows how to check the message at each of its message processing stages (before/after serialiization/deserialization).

To my surprise, the AfterSerialize stage is showing up twice in that log.  In the first invocation, my response looks good.  In the second invocation, I get the message 'Object reference not set to an instance of an object.', which seems to be thrown in Microsoft.Web.Services.WebServicesExtension.AfterSerializeServer(SoapMessage message).  

What's causing that second invocation?  And why does it only seem to occur over that box?

Conditions: WSE 1.0.3057.0, web service invoked from behind a firewall, over HTTPS, OS WS2003, IIS

From http://www.developmentnow.com/g/28_0_0_0_0_0/dotnet-framework-webservices-enhanc
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