Recently I noticed that recordings have been disappearing from my WD 2TB My Book Essential external hdd. I recorded the Hell on Wheels marathon on a VIP722 and then transferred them to the WD. Today I checked the WD and noticed that all the Hell on Wheels episodes were gone. The WD is almost full, on <50 GB left. This isn't the first time I've noticed this. I also lost a few movies. Any ideas what's happening?