Hi, I am accessing exchange server 2003 using a CDO concept running as a windows service, everything was fine till I saw an exception occurred all of a sudden described as follows. ErrorSystem.Runtime.InteropServices.COMException (0x80040108): [Collaboration Data Objects - [MAPI_E_INVALID_OBJECT(80040108)]] at System.RuntimeType.ForwardCallToInvokeMember(String memberName, BindingFlags flags, Object target, Int32[] aWrapperTypes, MessageData& msgData) at MAPI.Message.set_ReadReceipt(Object ) Any pointers to what I should check for in my code. I can post the code if required. Thanks, snands