Sure you can, but you need to remove everything first, from the Windows Control Panel, including the "FSDT Universal Installer" (if you use MSFS) and the "Addon Manager" (if you also use FSX or P3D), doing this will clear your previous folder choice, letting you to install anywhere.
It's perfectly fine choosing something like D:\Addon Manager, just don't select the root of a drive! And, be sure your drive is formatted in NTFS.