i connected my new Leonardo to my PC the first time yesterday. (Win 7 x64, IDE 1.0.1)
I had to install the driver manually using the device-manager.
All worked just fine for about 2 hours, but suddenly i couldn't upload sketches to my board anymore.
I took a look into the device manager, and the arduino were listed as "Unknown Device".
From then on, everytime i plug the board to my pc, the Arduino gets recognized as "Arduino Leonardo" for about 10 seconds, but then it switches to "Unknown Device".
I tired re-installing the drivers and such things, but i can't work with it either way.
Only have one cable with this particular connector, so no.
[quote author=Coding Badly link=topic=126736.msg953180#msg953180 date=1349980629]Have you tried a different USB port on the computer?[/quote]Not working with usb-hub nor direct to the mainboard-plugs.
I had a similar issue (device disconnects from windows after about 12 seconds after I uploaded a sketch), BUT, my device disapears entirely, (bing-bong) I don't have an "Unknown device"...