Update: Since my original post (below), I’ve got round the subject problem. A search for error code 46 gave me “path is invalid”. I therefore copied the external USB drive BU image to my data partition (P:) on notebook hard-drive and re-ran the restore using the copy as source. Restore successful. However, in order to restore from the original BU, I’m wondering whether it is necessary to alter boot sequence in BIOS, putting USB drive 1st (?). I’ll try in due course (I have other priorities), but if anyone already knows this works, I should be grateful to hear (to save me trialling).
Original: “My 1st test of CBU v3 restore of system partition C: has failed with error code 46. The image verifies as OK. I’ve run the restore process twice with same error code. The BU is a full (base) image stored on external USB drive. The recovery process commences OK during system boot, but then throws up the error code almost immediately.”