Did remove the Library folder? Close unity, remove the library folder, then open your project up again - (of course you'll need to wait a while for your project to re-load.)
If it worked before, it's probably a corruption of some kind in Library,
I lasted about 70 seconds. It wasn't clear at first that you are limited to a few lanes in the middle... maybe a line or something to differentiate. Very cute graphics. Loved it.
Very cool concept. I'm not sure if you used a Time.deltaTime type variable to control the speed of the things falling (it seems REALLY fast), but maybe allow another difficulty level.