Why Not?

I have been running into this issue lately since I restored my macbook from a Time Machine backup. The error says the following:

“This backup is too large for the backup volume. <space required for backup> is needed, but only <free space on disk> is available.”

This error is the result of a bug in Time Machine where it creates a full backup of your system after you restore your hard drive from a backup.

To fix this, you need to open your backup hard drive, delete the .sparsebundle file located on the drive, and do a new full backup. This will restart Time Machine to delete old backups as needed.