I have been backing up to dvd for 18 months. I do it weekly after tune-up runs. The last time I tried to backup it told me my disc was corrupt and I needed a new disc. I put in a new disc and now while it is compressing the data it stops and tells me I don't have enough free space on the hard drive - run disc cleanup to free up some space. This happens right after I run tune-up (which includes clean-up). On MY COMPUTER it shows like I have 37.2 G of free space. Any ideas what's happening here?