This backup is too large for the backup disk. The backup requires 35.72 GB but only 24.79 GB are available.
Estimated size of full backup: 149 GB
Size of Backups.backupdb on the Time Machine drive is 166 GB and there is 18GB of free space on the drive.
So why doesn't the backup go through? It should be able to delete old files… especially since the current backup size on the drive is less than it is required for the new one.