wcf - The security protocol cannot secure the outgoing message -

i trying return custom fault exception using unity following error during rst\issue action:

[service trace viewer exceptions][1]

image: [1]: http://i.stack.imgur.com/oaxgt.png

1. no signature message parts specified messages 'http://tempuri.org/iwcfservicelayer/getfirstorder' action.
2. the security protocol cannot secure outgoing message
3. requestcontext aborted

i using custmbinding resembles wshttpbinding. here manually throw exception in wcf method, in order test behaviour.

when comment out throw new exception statement, service works fine , returns expected results. service cannot handle exceptions currently. so why can't service secure outgoing message when exception occurs?

edit (bindingconfig):

  <custombinding>     <binding name="myservicebinding" closetimeout="00:05:00" opentimeout="00:05:00"       receivetimeout="00:05:00" sendtimeout="00:05:00">       <transactionflow />       <reliablesession maxpendingchannels="4000" maxretrycount="20"         maxtransferwindowsize="4000" ordered="false" />       <security enableunsecuredresponse="false" authenticationmode="secureconversation"         messagesecurityversion="wssecurity11wstrustfebruary2005wssecureconversationfebruary2005wssecuritypolicy11basicsecurityprofile10">         <secureconversationbootstrap authenticationmode="sspinegotiated"           messagesecurityversion="wssecurity11wstrustfebruary2005wssecureconversationfebruary2005wssecuritypolicy11basicsecurityprofile10" />         <localservicesettings maxstatefulnegotiations="500" maxpendingsessions="500" />       </security>       <textmessageencoding maxreadpoolsize="100" maxwritepoolsize="50" />       <httptransport maxreceivedmessagesize="2000000" allowcookies="true"         maxbuffersize="2000000" />     </binding>   </custombinding>