If you are still have downloading problems when you rollback and still are getting "Core" messages or downloader just wont show up heres what you do.

go to Start, then go to Run, type in MSCONFING, go to startup and you will see a box named "Core", click on the box so it will NOT startup...hit apply, then restart your cpu..ive had the core problem and figured this trick out and it works great with mine and other peoples pc's.