Time Machine Back up since 10.13.2

Since the recent upgrade (last two days) my MacBook Pro will not back up in time machine.

I get the error: The backup disk is not in Mac OS Extended (Journaled) format, which is required.

I've run Disk utility and it's fine and still extended Journaled format - I haven't change it.

There is plenty of room on the disk, nothing's changed that I know of.

What do you suggest?