That happens due to various reasons that I will list here:
The application is fake, and although it finds various things, it can't fix them, thus asking for payment to "unlock" this functionality. Uninstall it as fast you can.
It encountered a situation where the scanned file is locked by Windows and the application simply stops and even if it manages to finish the scan, it won't start.
I advise installing CCleaner to overcome these situations.