SoapExtension.GetInitializer exception

[Leor]

I am trying to add a soap extension to a web service. I am getting
the following error, and cannot figure out what cast is invalid. I am
using the sample "TraceExtension" class from the msdn web site:
http://tinyurl.com/59qmm
Any suggestions?

Thanks,
Leor Amikam

An unhandled exception of type
'System.Web.Services.Protocols.SoapException' occurred in
system.web.services.dll

Additional information: System.Web.Services.Protocols.SoapException:
Server was unable to process request. --->
System.InvalidCastException: Specified cast is not valid.
at System.Web.Services.Protocols.SoapReflectedExtension.GetInitializer(Type
serviceType)
at System.Web.Services.Protocols.SoapReflectedExtension.GetInitializers(Type
serviceType, SoapReflectedExtension[] extensions)
at System.Web.Services.Protocols.SoapServerType..ctor(Type type,
ProtocolsEnum versionsSupported)
at System.Web.Services.Protocols.SoapServerProtocol.Initialize()
at System.Web.Services.Protocols.ServerProtocol.SetContext(Type
type, HttpContext context, HttpRequest request, HttpResponse response)
at System.Web.Services.Protocols.ServerProtocolFactory.Create(Type
type, HttpContext context, HttpRequest request, HttpResponse response,
Boolean& abortProcessing)
--- End of inner exception stack trace ---