Time Machine Auto Backup fails silently. Property list invalid?

Hi,

After a recent reinstall, I can't seem to make Automatic Time machine backups anymore.

The backup disk is remote, and the backup is encrypted.

Manual backup works perfectly.

However, if I try to change the automatic backup switch in system preferences to on or off, nothing really happens except the position of the switch. In both positions, it keeps announcing "Next backup in an hour" (see below).

Looking at system.log, I only see the following warning:

Mar 7 16:53:50 my.machine.adress backupd[793]: Property list invalid for format: 200 (property lists cannot contain NULL)

I looked at the file /Library/Preferences/com.apple.TimeMachine.plist, and could not see any "NULL" value.

Following https://discussions.apple.com/thread/5509168 discussion on that error message, I checked the list of excluded folder, and indeed found one which didn't exist anymore. I excluded it, but the problem stayed.

I then Trashed the plist file, rebooted, reconfigured TimeMachine with 2 existing excluded folders. Pressing "Yes" for automatic backup, I got the message:

Mar 7 16:07:11 my.machine.adress UserEventAgent[11]: com.apple.backupd-auto launchd job enabled

Mar 7 16:07:11 my.machine.adress backupd[358]: Property list invalid for format: 200 (property lists cannot contain NULL)

Mar 7 16:07:12 my.machine.adress backupd[358]: Property list invalid for format: 200 (property lists cannot contain NULL)

Pressing "No", I got:

Mar 7 16:07:17 my.machine.adress backupd[358]: Property list invalid for format: 200 (property lists cannot contain NULL)

Mar 7 16:07:17 my.machine.adress UserEventAgent[11]: com.apple.backupd-auto launchd job disabled

Mar 7 16:07:17 my.machine.adress backupd[358]: Property list invalid for format: 200 (property lists cannot contain NULL)

Any idea how to cure this?