Lenovo T500 + Windows 7 + Unknown device
 

I just wanted to share my solution for a DisplayLink problem with you. Maybe it also works for others.

I have a Lenovo T500 with switchable graphics (ATI) running Windows 7 Prof. I recently bought a DisplayLink adapter to use a third monitor with my notebook. With switchable graphics enabled I installed the latest DisplayLink drivers, rebooted and connected the adapter. It worked immediately.

But when I booted my computer the next time, the adapter stopped working and everytime I connected it with my computer, Windows did not recognize the device and displayed an "Unknown device" message. I tried almost everything, but the adapter would just not be recognized (other usb-ports/cables, reinstalled the drivers, disabled switchable graphics, etc.).

But finally I fixed it! With switchable graphics disabled, I disconnected the DVI-side of the adapter from my monitor and connected it via USB only to my computer.... and now the adapter was recognized correctly by Windows! I plugged in the DVI cable again and the third monitor worked again. And since then it just works (however I did not yet try to reenable switchable graphics).

So if you're having such an "Unknown device" problem maybe you should try connecting the adapter without the DVI-cable plugged into the adapter. At least for me, that worked.

Ok, so here's an update regarding the "unknown device" problem: I'm using the Lenovo Advanced Mini Dock and whenever my notebook was undocked, the problem occurs at the next startup again. The fix with disconnecting the DVI-cable works, but it's still quite annoying und a driver update fixing this would be greatly appreciated. Well, at least it works.