did you just install the devices by plugging them in and running the drivers install for each device with a local admin account or something?
What i would do is i would try to plug only one in and make sure that comes up every time and works with your program on the machine. Then plug in more devices.. make sure that they are displaying in your devices list if your using windows 7. If one is not passing through or installing check to see if the Zero client see's and the OS see's it.
What view agent, connection server and firmware are you running (verison number).