Shouldn't there be 2 DLLs, a 32 bit default and a 64 bit via a proxy named SpriteAtlas_x64.dll. As it stands loading the yymps and blindly hitting run will error as you won't be on 64 bit runtime by default (you'll be in 32 bit mode - hence the error). See the "What If I Want To Make A 64bit DLL" section in the docs,