it has to be the same exact drive letter and drive name, and you had to back-up the rekordbox files that are explained in the topic you posted. I've done it twice from WinXP to Win7 & 8 with no problem at all, just make sure you copy the files correctly first- I used a program called "Extreme Copy Pro" that makes sure the files are in the exact same structure & location to ensure a flawless transition. Just to be safe I always back-up the rekordbox files in case the OS crashes or some disaster strikes the computer/laptop. There are soooo many tiny files rekordbox backs up (like artwork and beat-grid data for each track) it aint large files but there is at least one or two for each file you have in rekordbox- hence why backing it up might take some time.
Sorry to say but u might have to re-analyze ur beat grids- or import them from an external hard drive (with the playlist syncronize feature in rekordbox 2.1.1 or later)