Zalman VE200 - having issues booting via Virtual Drive

Hey y'alls, I have a Zalman VE-200 USB enclosure with a 64GB Crucial M4 SSD. I got the drive the for virtual drive, the feature that allows booting straight from ISOs. My problem is the virtual drive is hit or miss with me. I've found that when it works, it works wonderfully. But sometimes it just doesn't work. The enclosure will mount the ISO, but when I try and boot, it will either go entirely undetected (please insert bootable medium), or it will freeze. I've noticed this on an old Core 2 Duo HP Elitebook, and even older Dell Optiplexes (dual-core Pentium D).

Can some one help me out troubleshooting this issue? I've dug around but all I keep finding are reviews that praise the virtual drive feature, rather than troubleshooting tips.