I also get the error when running windows 7 x64
File: D:\Program Files\Paint.NET\Effects\Twainable.dll
Effect Name: Twainable.EffectPlugin
Full error message: System.BadImageFormatException: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)
at Dosadi.EZTwain.EZTwain.IsAvailable()
at Twainable.EffectPluginConfigDialog.CheckAvailableTwain()
at Twainable.EffectPlugin.CreateConfigDialog()
at PaintDotNet.Menus.EffectMenuBase.RunEffectImpl(Type effectType) in D:\src\pdn\paintdotnet\src\PaintDotNet\Menus\EffectMenuBase.cs:line 708