I'm getting the following error in my application:
Unable to serialize the session state.
In 'StateServer' and 'SQLServer' mode,
ASP.NET will serialize the session
state objects, and as a result
non-serializable objects or
MarshalByRef objects are not
permitted. The same restriction
applies if similar serialization is
done by the custom session state store
in 'Custom' mode.
Really, you should mainly be storing your own state data / objects (ideally modelled as DTO classes), in which case the answer is: any you mark as
ISerializable. You shouldn't be adding raw UI controls or other unknown objects to session-state. In particular, for reasons like this, which had a major performance impact on an app the other day.