i got the same thing. Here are the details
File: E:\Paint.net\Effects\Vandermotten.PaintDotNetEffects.dll
Effect Name: Vandermotten.PaintDotNetEffects.DropShadowEffect
Full error message: System.MethodAccessException: PaintDotNet.ColorWheel..ctor()
at Vandermotten.PaintDotNetEffects.DropShadowConfigDialog.InitializeComponent()
at Vandermotten.PaintDotNetEffects.DropShadowConfigDialog..ctor()
at Vandermotten.PaintDotNetEffects.DropShadowEffect.CreateConfigDialog()
at PaintDotNet.Menus.EffectMenuBase.RunEffect(Type effectType)
It was'nt happening sometime before :?
Maybe its a problem with Paint.NET V.3.31?