OK, here's the deal. I have an external HD I use for Time Machine backups that's 270GB. My internal that Time Machine is backing up is 250GB. For the past few days, Time Machine keeps giving me an error saying that it doesn't have enough room to backup anything. I know it keeps copies of stuff, but I thought it started erasing old copies as soon as the external was full. Is this not the case? Can anybody tell me what I might be doing wrong? Thanks in advance!