I have some 3.5 desktop drives in USB 3.5" enclosures. Recently I've started having a problem with them. Every so often the drives won't mount. I get an error with USB device in the Hardware Manager. If I remove the drive from the enclosure and put it on an IDE channel then its picked up ok. It also works fine when I put it back in the USB enclosure. But then after a while the drive refuses to mount again. I've not lost any data with this yet. But it only a matter of time. Since I use the USB drives as part of backup routine.
Any ideas? Generally I just turn the drives off when I turn the desktop or laptop off. Theres no other way to unmount it.