Same issue here. If the problem lies in the Update.esm, there's nothing we can really do, eh? Great. <3 Bethesda so much right now. 20 bucks for a file to break my game. I could have done that on my own for free. Edit: I rolled back to 1.6, and it fixed the attacking problem. I haven't played for very long though, so all I know is Dawnguard is active in my load order and I can attack again. I don't know if there are any long term issues or if Dawnguard even actually works with this patch version, but this will have to do until they patch it.