[0.31.1] Game crashes when pressing mouse wheel button/middle button

[fokwi]

The title says it all

Pokémon 3D has crashed!
---------------------------
 
System specifications:
Pokémon 3D version: 0.31.1
Operating system: Microsoft Windows 7 Ultimate  [6.1.7600.0]
Decimal seperator: ,
---------------------------
 
Here is further information:
Message: Object reference not set to an instance of an object.
InnerException: NOTHING
BaseException: Object reference not set to an instance of an object.
HelpLink: No helplink available.
Data: System.Collections.ListDictionaryInternal
Source: 2.5DHero
TargetSite: Name: Movement [
  Attributes: PrivateScope, Private
  CallingConvention: Standard, HasThis
  ContainsGenericParameters: False
  DeclaringType: _2._5DHero.OverworldCamera
  IsAbstract: False
  IsAssembly: False
  IsConstructor: False
  IsFamily: False
  IsFamilyAndAssembly: False
  IsFamilyOrAssembly: False
  IsFinal: False
  IsGenericMethod: False
  IsGenericMethodDefinition: False
  IsHideBySig: False
  IsPrivate: True
  IsPublic: False
  IsSecurityCritical: True
  IsSecuritySafeCritical: False
  IsSecurityTransparent: False
  IsSpecialName: False
  IsStatic: False
  IsVirtual: False
  MemberType: Method
  MetadataToken: 100664247
  MethodHandle: System.RuntimeMethodHandle
  Module: 2.5DHero.exe
  ReflectedType: _2._5DHero.OverworldCamera
  ]
 
StackTrace:    at _2._5DHero.OverworldCamera.Movement()
  at _2._5DHero.OverworldCamera.Update()
  at _2._5DHero.OverworldScreen.Update()
  at _2._5DHero.Basic.Update(GameTime gameTime)
  at _2._5DHero.DGame.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 Microsoft.Xna.Framework.Game.Run()
  at _2._5DHero.Program.Main(String[] args)