Why does my Speedgoat IO333-410K disappear?

I'm using several Speedgoat systems with IO333-410K boards installed. I intermittently get an error when I try to load code on the Speedgoat machine. The machine refuses to recognize the existence of the board. So far, I've been able to "fix" the problem with a reboot (sometimes several reboots), but I'm concerned. This problem is not with just with one machine; rather, I've seen it on three systems. Anyone know what's going on? Anyone know what to do about it?