Recuva not recovering?

Don't get me wrong, Recuva is well designed, easy to use, simple.

But on a laptop recently, that had windows installed over a pre-existing windows install (repair install), Recuva found 0 recoverable files!.

http://www.handyrecovery.com/ that program found & was able to recover from 50% to 80% of the files I was wanting to recover off the drive.

What gives?

Why did Recuva find 0 & that program found it all?

Thanks!