I was having that same problem too, but you're not gonna like the answer...
I copied everything I wanted to keep to my external HD (including a copy of the most recent installer) and then restored to factory settings.
There's a dude here
who uploaded his netmarble folder, maybe try deleting yours and using that first, but otherwise you're probably gonna have to format.
Also make sure if you run McAfee or Norton that they're disabled when you're patching.