Please advise me to remove "wsu:Timestamp" in SOAP Header. (WSE 2.0 for Framework 1.1)

Hi all,

I use WSE 2.0 for Framework 1.1 to add UsernameToken to SOAP Header.

I have a problem about SOAP Header. I try to use customer myclass (inherites from "SoapOutputFilter" class) to remove "//wsse:Security/wsu:Timestamp".

public override void ProcessMessage(SoapEnvelope envelope)
{
            //removing Addressing headers from the outgoing request
            XmlNode securityNode = envelope.Header["//wsse:Security/wsu:Timestamp"];
            envelope.Header.RemoveChild(securityNode);
 }

but the error "Object Reference not set" is occurred.

Please advice me, how can I remove "wsu:Timestamp" node in SOAP Header?

Thank you very much