callback function cannot accept object as a parameter

I found if I defined callback method like

void  call(object o)

I will received the following error

Unhandled Exception: System.ServiceModel.CommunicationObjectFaultedException: The communication object, System.Se开发者_StackOverflow社区rviceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state.

if using

void call(string s)

then it is good. Anyone knows the reason.

Yes you can't use object type. Operations (including callbacks) always have to know exact type of parameter otherwise they are not able to perform serialization and deserialization.