"Failed to read snapshot manager drive"

Ok, long time TIH user who's just updated to 2012 from 2011. I dual-boot Windows XP and ubuntu (on a separate, EXT3-formatted partition), with my media files on separate EXT formatted partitions (4 physical drives in total)

Now, when I try to image either Windows or Linux to an NTFS formatted partition on a 3rd drive, I get a succession of "Failed to read hard disk sector -4,000,000 on disk 1 (or 2, or 3 or 4)" type errors, along with "failed to read snapshot manager drive" and no backup.

I've checked the various filesystems (using gparted and chkdsk /f), no problems found. I've re-fomatted the target disk.

I've un-installed / re-installed several times, and even tried going back to v. 2011, which now gives me the same errors (and didn't before).

I've successfully completed backups using another product (Todo) for both the Windows and ubuntu partitions - so it doesn't look like there's a terminal problem with my discs. My question is - is there anything I can do to fix the TIH problem?

I bought the 2012 upgrade at Halloween (impulse purchase, based on the discounted price), and am now regretting it. Too late for a refund, no evident way forward...