SDV 1.1 crash

Message: There was an error generating the XML document.
InnerException: System.InvalidOperationException: There was an error generating the XML document. ---> System.InvalidOperationException: The type StardewValley.Objects.SpecialItem was not expected. Use the XmlInclude or SoapInclude attribute to specify types that are not known statically.
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterObject.Write15_Item(String n, String ns, Item o, Boolean isNullable, Boolean needType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterObject.Write29_Chest(String n, String ns, Chest o, Boolean isNullable, Boolean needType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterObject.Write35_Object(String n, String ns, Object o, Boolean isNullable, Boolean needType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterObject.Write36_Object(Object o)
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id)
   at StardewValley.SerializableDictionary`2.WriteXml(XmlWriter writer)
   at System.Xml.Serialization.XmlSerializationWriter.WriteSerializable(IXmlSerializable serializable, String name, String ns, Boolean isNullable, Boolean wrapped)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterSaveGame.Write89_GameLocation(String n, String ns, GameLocation o, Boolean isNullable, Boolean needType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterSaveGame.Write131_SaveGame(String n, String ns, SaveGame o, Boolean isNullable, Boolean needType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterSaveGame.Write132_SaveGame(Object o)
Stack Trace:    at System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id)
   at StardewValley.SaveGame.<getSaveEnumerator>d__45.MoveNext()
   at StardewValley.Menus.SaveGameMenu.update(GameTime time)
   at StardewValley.Game1.updateActiveMenu(GameTime gameTime)
   at StardewValley.Game1.Update(GameTime gameTime)
   at Microsoft.Xna.Framework.Game.Tick()
   at Microsoft.Xna.Framework.Game.HostIdle(Object sender, EventArgs e)
   at Microsoft.Xna.Framework.GameHost.OnIdle()
   at Microsoft.Xna.Framework.WindowsGameHost.RunOneFrame()
   at Microsoft.Xna.Framework.WindowsGameHost.ApplicationIdle(Object sender, EventArgs e)
   at System.Windows.Forms.Application.ThreadContext.System.Windows.Forms.UnsafeNativeMethods.IMsoComponent.FDoIdle(Int32 grfidlef)
   at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
   at System.Windows.Forms.Application.Run(Form mainForm)
   at Microsoft.Xna.Framework.WindowsGameHost.Run()
   at Microsoft.Xna.Framework.Game.RunGame(Boolean useBlockingRun)
   at StardewValley.Program.Main(String[] args)