After my backup runs to 14% completion, it ends in the progress box with "Device I/O error (source Hard disk manager)". The messages before that are "Cmp volumes... Write changed sectors... Write clusters...". Looking in the log file stubact.log, I find under "[Result]" the following lines: [Result] Error: 69648 (0x11010) Device I/O error The error is repeatable: when I run it again, it reappears. Chkdsk doesn't report any error. Windows eventlog doesn't seem to show any out of the ordinary. I made the earlier full backup with Paragon Hard Disk Manager Suite. I was doing the incremental with Premium because Suite doesn't seem to have the capability to adhere to the exclusion list of the original full backup (making the incremental very large). The Suite didn't raise this error, only Premium edition does. All software is up-to-date, drivers are up-to-date and system has been recently restarted. Running Windows 7, 2x Xeon X5680 @3.33Ghz, 48MB memory, 3x 2TB disks in hardware RAID-0, 2TB backup disk separate, but internal. All disks same type, WD20EARS from Western Digital. I can't find anything on error 0x11010 on Google or on these forums. It doesn't appear to be a bad sector. Any ideas?