I could really cry about now. I recently updated Kindle 4 PC to 1.6.0 for the collections. I spent 3 days making them and got everything sorted nicely. Tonight I ran my cleaning programs and when I went to download my latest purchase...It had de-registered!
This means my 700+ books now wont open. I've lost my collections and

I had to spend the past two hours removing each book.
I then ran each cleaner program till it happened again. Then went into my manage Kindle page and remove the extras devices and now have no Kindle books on my PC
I want to save others the heartache I just went through. If you use Kindle For PC 1.6.0+ do not run ATF-Cleaner It will de-registered Kindle For PC by removing something needed.
ATF-Cleaner is a very small free cleaner program I've used for years. I've never had a problem before I upgraded. Needless to say I've removed it. It's a good thing it's not a real popular program like CCleaner which I also use but man this sucks!