I am having the same -5000 issue, I agree with the other posters who have pointed out that disabling security programs is NOT the correct answer ultimately. It may work, but it forces the user to compromise their system security during the update. There is absolutely nothing about copying files off a USB device which should run afoul of AV unless Apple is doing stupid things.
Hey Apple, this Ipad was purchased by my empolyer for company use and I don't have control over individual PC security software as I am not admin. Therefore I CANNOT UPDATE MY IPAD because I do not have permission to disable AV software. Big fail.
Oh and by the way, it's 2012 so providing error reports using integers (and negative ones still, really?) is ridiculous. This isn't the old LCII machine, you have PLENTY of memory to put descriptive error strings in your code, use them. Don't make me use Google to search for your stupid error codes when they could and should be human readable.