I have a Tablo dual lite, not refurbished. I occasionally go to watch a program that I intended to record and get a message that there is no external storage available. I go to the tablo and hard reset it (pull the power cord) wait 30 seconds and it now sees the hard drive again. I am not sure what’s going on here, but it’s frustrating to think you have recorded something, only to find out it was not recorded due to this problem. This seems to happen every 8-10 days, mostly overnight so I loose the morning news cast.
What drive is it? Also, weak power supplies, if the drive is being powered through the USB cable, can cause all sorts of weird issues. You can either get another drive with it’s own supply, or get one of those split USB cables that lets you separately power a device.
I would check to see if the hard drive has a firmware update available.