title: Unable to serialize the session state
body: <p>When putting my application on a web server and trying to 'log in' I get the following error:</p>
  
  <pre><code>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 'Gebruiker' in Assembly 'App_Code.qzuhycmn, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' is not marked as serializable.]
     System.Runtime.Serialization.FormatterServices.InternalGetSerializableMembers(RuntimeType type) +9452985
     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) +218
     System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.Serialize(Object obj, ISurrogateSelector surrogateSelector, StreamingContext context, SerObjectInfoInit serObjectInfoInit, IFormatterConverter converter, ObjectWriter objectWriter, SerializationBinder binder) +54
     System.Runtime.Serialization.Formatters.Binary.ObjectWriter.Serialize(Object graph, Header[] inHeaders, __BinaryWriter serWriter, Boolean fCheck) +542
     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) +1708
  
  [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) +1793
     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[]&amp; buf, Int32&amp; length, Boolean compressionEnabled) +67
     System.Web.SessionState.OutOfProcSessionStateStore.SetAndReleaseItemExclusive(HttpContext context, String id, SessionStateStoreData item, Object lockId, Boolean newItem) +114
     System.Web.SessionState.SessionStateModule.OnReleaseState(Object source, EventArgs eventArgs) +807
     System.Web.SessionState.SessionStateModule.OnEndRequest(Object source, EventArgs eventArgs) +184
     System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +148
     System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&amp; completedSynchronously) +75
  
  
  Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.1 
  </code></pre>
  
  <p>The only thing I do there with Sessions is this: </p>
  
  <ul>
  <li>Session["Rechten"] = "GlobaalAdmin"; (example)  </li>
  <li>Session["gebruikerid"] = txtID.Text; (the ID they log in with)</li>
  <li>And redirect them to another page: Response.Redirect("LoggedIn.aspx",true);</li>
  <li><a href="http://pastebin.com/jZprwA8m" rel="noreferrer">http://pastebin.com/jZprwA8m</a> (Putting the gebruiker into a session)</li>
  </ul>
  
  <p>There have been multiple topics about this problem but none of them seem to have helped me.
  Everything works locally, but online it doesn't.</p>