InstanceContext Mode.Single + OperationContex t.Current

[sandrofurlan]

Hi all,
i have a WCF service for USB communication. I need to instance it as a
singleton class so i do:

<ServiceBehavio r(InstanceConte xtMode:=Instanc eContextMode.Si ngle, _
ConcurrencyMode :=ConcurrencyMo de.Multiple)_
Public Class myService

....

End class

And that's OK! But I also need do define callbacks to signal events so
I add a callback Interface and:

<ServiceContrac t(NameSpace:="h ttp://Microsoft.Servi ces", _
SessionMode:=Se ssionMode.Requi red, _
CallbackContrac t:=GetType(ImyC allback))_
Public Interface IService

...

end Interface

The problem is in the constructor method of Service'class where I've
to get the InstanceContext for the CallbackChannel . I got an exception
in this code:

public sub new

callback = OperationContex t.Current.GetCa llbackChannel(O f
IEasyBusCallbac k)() '<-Reference to an object not set up on an object
request

end sub

Note that class myService inherits another class that implements
communication

thanks