I upgraded my MacBook Pro to Snow Leopard, and made some other changes that have caused my next Time Machine backup to be quite large. Previous to the upgrade my backup drive had filled up, so Time Machine was deleting old backups to make room for new ones. When Time Machine started the first backup after the upgrade, it displayed a message that it was freeing up space. But it wasn't able to free up enough:
(The disk has 320 GB capacity.)
How can I free up more space on the disk (without reformatting or deleting all the existing backups)? I don't want to recklessly delete files and take the risk of confusing Time Machine.