Time machine failure - on both machines after working for 2 months

I have 2 apple macbooks doing backups to my mirror device.

Both have been doing hourly backups without problem for over 2 months.

I can use time machine and view the backups to when I installed it.

However all of a sudden I am getting this message on BOTH macbooks.

Screen Shot 2015-02-18 at 08.00.57.png

I dont really want to delete 2 1/2 months of back ups but thats what its telling me to do on BOTH machines.

I have rebooted the mirror drive and still getting same error.

any idea’s ?

thanks

Something must have corrupted the backup. Was your WD My Cloud Mirror disconnected by mistake at any point?

No, nothing was disconnected.

Both time machine backups have failed.

Just as a side note to this, speaking to my son who as the “mycloud” not the mirror.

His timemachine turns out to have been failing at least once a week and he is having to redo it all again weekly.

Exactly the same error.

(he lives 1500 miles away so not on same network at all).

Seems to be a pattern here if I look through older posts.

WD and apple do not seem to mix that well.