Yeah, there's too many factors that could be exploited. Hackers for one- say what you will, but I guarantee if voting goes online, they'll find a way to manipulate it.
All kinds of technical glitches I can't even think of are a possibility as well.
Although.. I think the result would just be delayed voting because of this - if somebody hacked into the system and messed things up or even made a subtle change, I'm sure it would get detected.