Bought a new Mac Mini and migrated from my Time Machine backup. I then read this with some optimism: http://www.macworld.com/article/1161421/migrate_time_machine_backup_to_new_mac_in_lion.html

I do not however get any such options. On the new Mac Time Machine refuses to backup because there is not enough space on the drive.

How can I get t to continue using the existing backup, or alternatively: how can I get rid of all the data on the backup drive and start a new bacup?

OK, I finally believe I have solved it: continuing to use the old backup from the previous OS just isn't possible no matter what an article says.

So plan B went into effect and after a lot of struggling I was finally able to erase the disk completely and start it of on a fresh backup from my new Mac (that has all the old files anyway).

Case closed.