Hmm. As Tiny says, WD drivers shouldn't be an issue. On Macs at least, you just format and go.

I'd be inclined to invest in a new Ext HDD - you can get 2tb rugged USB3 LaCie's for £65. Since the old drive is still readable, you would still have the archive if you need it (plus you can never have too many backups).

Thanks Both - looks like it might be a fault on the drive then? I had another failure when I was away this morning and the next one that just finished was ok. Didn't even touch the drive. Drive I am using at present is a WD My Passport, its being used as backup since last June and before then as a backup for my photos on a desktop.

I'd say it is certainly not reliable as a backup anymore. Time for a new drive.

It might be worth launching the mac in recovery mode (hold down cmd-R while booting) and running disk utilities over the start up drive, just to be safe. It take sages, though...