I used unetbootin-windows-583 and Universal-USB-Installer-220.127.116.11 for BT5R3 and come up with this every time. I have tried a different flash drive as well and it has worked on this computer previously although now it doesn't seem to want to anymore.
It brings me to BackTrack Text - Default Boot Text Mode, Stealth, Forensics, ect. After selecting I get this screen. Tried to figure it out but haven't had any results the BT5R3 file works on VMware.