Invalid Session Fault with Token Based Authentication

Should I be receiving an Invalid Session Fault with a message that says "Your connection has time out. Please log in again." when using token based authentication.   My webservices were running fine until suddenly the Invalid Session Fault was thrown even though 2 seconds earlier a webservice call was successful.

My only thought is we are calling this immediately before we set the token in the header. Could it be causing a problem?

            // setup the headers to ignore read only fields              NetSuiteBindingStub stub = (NetSuiteBindingStub) port;              stub.clearHeaders();                 SOAPHeaderElement prefHeader =   new SOAPHeaderElement("urn:messages.platform.webservices.netsuite.com", "Preferences");              Preferences prefs = new Preferences();              prefs.setIgnoreReadOnlyFields(new Boolean(true));              prefHeader.setObjectValue(prefs);              stub.setHeader(prefHeader);