R – AsyncFileUpload SerializationException

I'm using the AsyncFileUpload control to upload images.
It works fine from localhost, but when I uploaded it on server I get the following error.

I can't even understand the reason of this error. I'll appreciate any answer.

This is the Method that I'm using

protected void AsyncFileUpload1_UploadedComplete(object sender, AjaxControlToolkit.AsyncFileUploadEventArgs e) 
{
    string email = WriteYourEmailTXT.Text;
    var dt = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day).ToString("ddMMyyyy");
    string parentFolder = Server.MapPath("uploads");
    string childFolder = parentFolder + "\\" + email + "\\";
    if (!Directory.Exists(childFolder))
        Directory.CreateDirectory(childFolder);

    string counter = getCount();
    if (AsyncFileUpload1.HasFile) {
        string ext = getExtension(AsyncFileUpload1.FileName);
        string finalName = dt + "_" + counter + ext;
        string finalPath = childFolder + finalName;
        AsyncFileUpload1.SaveAs(finalPath);
        SetCount();
        SetFileName(finalName);
    }
}

protected void SetCount() 
{
    HttpCookie aCookie = Request.Cookies["CountPhoto"];
    int cookieNum = 0;
    if (aCookie != null)
        if (aCookie.Value != "")
            cookieNum = int.Parse(aCookie.Value.ToString());

    string newvalue = (cookieNum + 1).ToString();
    Response.Cookies["CountPhoto"].Value = newvalue;
}

protected void SetFileName(string fileName) 
{
    HttpCookie aCookie = Request.Cookies["FileName"];
    var filename = "";
    if (aCookie != null)
        if (aCookie.Value != "") {
            filename = aCookie.Value;
        }
    string newFileName = filename + "," + fileName;
    Response.Cookies["FileName"].Value = newFileName;
}

Error

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.

Stack Trace: [SerializationException: Type
'System.Web.HttpPostedFile' in
Assembly 'System.Web, Version=2.0.0.0,
Culture=neutral,
PublicKeyToken=b03f5f7f11d50a3a' is
not marked as serializable.]
System.Runtime.Serialization.FormatterServices.InternalGetSerializableMembers(RuntimeType
type) +7733643
System.Runtime.Serialization.FormatterServices.GetSerializableMembers(Type
type, StreamingContext context) +258
System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.InitMemberInfo()
+111 System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.InitSerialize(Object
obj, ISurrogateSelector
surrogateSelector, StreamingContext
context, SerObjectInfoInit
serObjectInfoInit, IFormatterConverter
converter, ObjectWriter objectWriter)
+161 System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.Serialize(Object
obj, ISurrogateSelector
surrogateSelector, StreamingContext
context, SerObjectInfoInit
serObjectInfoInit, IFormatterConverter
converter, ObjectWriter objectWriter)
+51 System.Runtime.Serialization.Formatters.Binary.ObjectWriter.Serialize(Object
graph, Header[] inHeaders,
__BinaryWriter serWriter, Boolean fCheck) +410
System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize(Stream
serializationStream, Object graph,
Header[] headers, Boolean fCheck) +134
System.Web.Util.AltSerialization.WriteValueToStream(Object
value, BinaryWriter writer) +1577

[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) +1662
System.Web.SessionState.SessionStateItemCollection.WriteValueToStreamWithAssert(Object
value, BinaryWriter writer) +34
System.Web.SessionState.SessionStateItemCollection.Serialize(BinaryWriter
writer) +606
System.Web.SessionState.SessionStateUtility.Serialize(SessionStateStoreData
item, Stream stream) +239
System.Web.SessionState.SessionStateUtility.SerializeStoreData(SessionStateStoreData
item, Int32 initialStreamSize, Byte[]&
buf, Int32& length) +72
System.Web.SessionState.OutOfProcSessionStateStore.SetAndReleaseItemExclusive(HttpContext
context, String id,
SessionStateStoreData item, Object
lockId, Boolean newItem) +87
System.Web.SessionState.SessionStateModule.OnReleaseState(Object
source, EventArgs eventArgs) +560
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
+68 System.Web.HttpApplication.ExecuteStep(IExecutionStep
step, Boolean& completedSynchronously)
+75