Unable to serialize the session state 'System.Web.SessionState.HttpSessionState' - asp.net

Question

Getting "Unable to serialize the session state" error, where I'm trying to store HttpSessionState object in Session. Below is my code which is causing issue. Since HttpSessionState is not serializable class and trying to put into session.
Public Shared Property CurrentSession As HttpSessionState
Get
Return TryCast(HttpContext.Current.Session("CurrentSessionObject"), HttpSessionState)
End Get
Set(value As HttpSessionState)
HttpContext.Current.Session("CurrentSessionObject") = value
End Set
End Property
Server Error in '/' 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.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Web.HttpException: 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.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[SerializationException: Type 'System.Web.SessionState.HttpSessionState' in Assembly 'System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' is not marked as serializable.]
System.Runtime.Serialization.FormatterServices.InternalGetSerializableMembers(RuntimeType type) [phone]
System.Runtime.Serialization.<>c__DisplayClass9_0.b__0(MemberHolder _) +42
System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory) +73
System.Runtime.Serialization.FormatterServices.GetSerializableMembers(Type type, StreamingContext context) +186
System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.InitMemberInfo() +166
System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.InitSerialize(Object obj, ISurrogateSelector surrogateSelector, StreamingContext context, SerObjectInfoInit serObjectInfoInit, IFormatterConverter converter, ObjectWriter objectWriter, SerializationBinder binder) +187
System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.Serialize(Object obj, ISurrogateSelector surrogateSelector, StreamingContext context, SerObjectInfoInit serObjectInfoInit, IFormatterConverter converter, ObjectWriter objectWriter, SerializationBinder binder) +53
System.Runtime.Serialization.Formatters.Binary.ObjectWriter.Serialize(Object graph, Header[] inHeaders, __BinaryWriter serWriter, Boolean fCheck) +571
System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize(Stream serializationStream, Object graph, Header[] headers, Boolean fCheck) +137
System.Web.Util.AltSerialization.WriteValueToStream(Object value, BinaryWriter writer) +1644
[HttpException (0x80004005): 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.]
System.Web.Util.AltSerialization.WriteValueToStream(Object value, BinaryWriter writer) +1733
System.Web.SessionState.SessionStateItemCollection.WriteValueToStreamWithAssert(Object value, BinaryWriter writer) +36
System.Web.SessionState.SessionStateItemCollection.Serialize(BinaryWriter writer) +652
System.Web.SessionState.SessionStateUtility.Serialize(SessionStateStoreData item, Stream stream) +246
System.Web.SessionState.SessionStateUtility.SerializeStoreData(SessionStateStoreData item, Int32 initialStreamSize, Byte[]& buf, Int32& length, Boolean compressionEnabled) +65
System.Web.SessionState.SqlSessionStateStore.SetAndReleaseItemExclusive(HttpContext context, String id, SessionStateStoreData item, Object lockId, Boolean newItem) +138
System.Web.SessionState.SessionStateModule.OnReleaseState(Object source, EventArgs eventArgs) +589
System.Web.SessionState.SessionStateModule.OnEndRequest(Object source, EventArgs eventArgs) +9947060
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +144
System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) +50
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +73

Answer 1

You need to mark the type/s your pushing in to SessionState as serializable, with the [Serializable] attribute.