it went something like:
1. corrupt config75.dat - lost client and backup sets.
2. recovered previous config75.dat from backup.
3. all local HD backups then reported " -645 chunk file damaged during save" error.
4. removed config75.dat and .bak then rebooted. relicenced and started from scratch (one empty backup set, one new script). same errors only - no complete execution of backup of local HDs.
lots of KB reading and forum browsing later, still no solution. couple of gems in the KBs, which I might post for fun on another post, but not worth the effort re fixing this problem.
let filemon and regedit loose on the problem (www.sysinternals.com - now MS owned). showed a bunch of .dat files in the folder:
all users\application\retrospect\rtrsec.dir\
and "my computer.dat" being accessed extensively during each failed execution.
we had nothing to lose, as next step was full uninstall, wipe and reinstall, so we shut down retrospect, and dumped the rtrsec.dir folder, and the rtrexec.dir folder for good measure.
restarted and the script finally executed to completion.
seems the corruption was in the 'my computer.dat' file (310MB), and not the config75.dat as most of the KB and forum threads indicated.
I think I would be inclined to move this folder first in similar circumstances, rather than dump your client and backup set configurations (config75.dat). you can always put it back again if there is no joy.
hope this saves someone more time than the KB did me.
cheers
lewis