I'm having the same issue. Whenever I try to copy the D3DX9_42.dll file Rocksmith crashes on startup, even though the default d3dx9_42 works perfectly with my game. I've tried to run in Compatibility mode for Win 7 and Run as Admin but still no luck. Any help would be greatly appreciated. EDIT: Got it to work with updating DirectX. http://forums.steampowered.com/forums/showthread.php?t=1218203