Hm, I'm having a problem with time machine. I have an external hard drive that I use for it. I unplugged the external hard drive for awhile, then plugged it back in. But when I plugged it back in, it now says that Time Machine can't back up because there is not enough space - even though the space is taken from previous Time Machine back-ups! Why is it not recognising its own back-ups on the external hard drive and how can I fix this?