Unable to serialize the session state

Question

While executing a .aspx page i am getting the following error. Can you please let me know how can i solve it.

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.UI.WebControls.DropDownList' 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) +9472709
   System.Runtime.Serialization.FormatterServices.GetSerializableMembers(Type type, StreamingContext context) +247
   System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.InitMemberInfo() +160
   System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.InitSerialize(Object obj, ISurrogateSelector surrogateSelector, StreamingContext context, SerObjectInfoInit serObjectInfoInit, IFormatterConverter converter, ObjectWriter objectWriter, SerializationBinder binder) +491
   System.Runtime.Serialization.Formatters.Binary.ObjectWriter.Write(WriteObjectInfo objectInfo, NameInfo memberNameInfo, NameInfo typeNameInfo) +388
   System.Runtime.Serialization.Formatters.Binary.ObjectWriter.Serialize(Object graph, Header[] inHeaders, __BinaryWriter serWriter, Boolean fCheck) +444
   System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize(Stream serializationStream, Object graph, Header[] headers, Boolean fCheck) +133
   System.Web.Util.AltSerialization.WriteValueToStream(Object value, BinaryWriter writer) +1762

[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) +1847
   System.Web.SessionState.SessionStateItemCollection.WriteValueToStreamWithAssert(Object value, BinaryWriter writer) +34
   System.Web.SessionState.SessionStateItemCollection.Serialize(BinaryWriter writer) +638
   System.Web.SessionState.SessionStateUtility.Serialize(SessionStateStoreData item, Stream stream) +244
   System.Web.SessionState.SessionStateUtility.SerializeStoreData(SessionStateStoreData item, Int32 initialStreamSize, Byte[]& buf, Int32& length, Boolean compressionEnabled) +67
   System.Web.SessionState.SqlSessionStateStore.SetAndReleaseItemExclusive(HttpContext context, String id, SessionStateStoreData item, Object lockId, Boolean newItem) +140
   System.Web.SessionState.SessionStateModule.OnReleaseState(Object source, EventArgs eventArgs) +807
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +148
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75

Thanks

Notification

As the message states, you may have added a non serializable object in the session state. Please that everything you put in the session is properly serializable, either by adding the [Serializable] attribute or by implementing IXmlSerializable – Trichinosis

Tip for other confused travelers: Search for Session[ and you might find the offending row. It will not stop directly where it fails. The answers are correct tough, as to what the error involves. – Shouse

Answer 1

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.

This line is pretty telling. You need to mark objects with [Serializable] to serialize the object (the MSDN link contains more details about serializing the object graph).

Earthling

I have already add <Serializable()> attribute. But error has occured: [SerializationException: Type 'System.Web.UI.WebControls.DropDownList' in Assembly 'System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' is not marked as serializable.] Please can you advise to solve this issue. Thanks – Notification

Why is it trying to serialize the DropDownList, which is a web control? I think it's trying to serialize the view, instead of the object, or do you have a DropDownList in your control? – Earthling

Note in the MSDN documentation, it says all complex objects that are children of the Serializable object must also have the [Serializable] attribute defined too. – Earthling

While executing a first time .aspx page i am getting that error. and then refresh that page was executed correctly. Pleace can help me. Thanks. – Notification

Can you post the definition of the class that's giving you problems? – Earthling

Answer 2

In my case, I was trying to serialize the non-serialized object that is HttpResponse. So this couldn't help me.

Check this if this couldn't solve your problem: Asp.net serialization error for session state

This post save my time and solved my problem.

Bettencourt

Answer 3

Add the following attribute to the offending class:

[Serializable()]

If that doesn't work then:

Consider using mode="InProc". I ran into this issue by switching to "SQLServer" and rolling back to "InProc". This might fix the issue because InProc doesn't require objects to be Serializable.

Which one is better, InProc or SQL Server, for Session State mode in asp.net?

Arun

Answer 4

[Serializable()]
public partial class CustomersMaintLog
{

Lucubrate