Can't Get Three USB Monitors to Work

[WilliamCall]

I've got a desktop computer with Windows 7/64 OS and a Radeon HD 6990 graphics card. I added two USB monitors several months ago (Lilliput UM-80), and everything went well. So, I decided to add a third USB monitor (Lilliput UM-70/c/t), unfortunately, I can't get all three to play at one time. I can get any two of the three to play, but when I try to install the third USB monitor, Win 7 is stuck in a "do-loop", that is, it asks me to restart my computer for the changes to take effect. When I restart my computer, the installation starts all over again. When I turn off or disconnect the third USB monitor, everything is normal.
I'm certain that the DisplayLink software is installed correctly, and all three monitors are connected to the same powered USB HUB. One thing that looks strange is the device IDs are the same. I currently have one UM-80 and one UM-70 monitor active (shouldn't the device IDs be different?). I'd appreciate any help/guidance. Thanks!