I have issues too on S-OFF rooted HTC EVO $G LTE. Busybox Pro first reboots the system. Then when I run it again, and do an install or a smart install, it scrolls a list of apps by, and pops up saying "It looks like the install failed. Try a different location"
I tried nin and ninx with the same result, and also tried busybox installer.
I have 80 MB free in /system.