Lately it seems that Time Machine has been underestimating the size of each backup. What it originally says to be a 10 MB backup turns out to be several GB. As it's backing up, Time Machine will say "X out of 10MB backed up" or something along those lines, but when X reaches 10MB, X continues to grow and so does the original estimate of 10MB. It might then say "13MB of 13MB backed up" and it will continue on this way until it has backed up so much underestimated data that Time Machine tells me it can't finish the backup because it doesn't have enough space on the backup drive. (Time Machine should've deleted some backups beforehand to make space for the new backup, but it didn't know to because it had underestimated the amount of space necessary for the backup.) I have already wiped the backup drive and deleted all the Time Machine preference files, only to still face the same problem. I'm backing up my internal 1TB drive (only 300 GB used) and my 500GB external drive (400GB used) to another 1TB external drive, so having enough space on the backup drive shouldn't be the problem, right? BTW, I'm running Snow Leopard. Any help is appreciated!