The symptoms this time were different to those I reported in January.
backupdseemed to be complaining about an inability to move a single file: a preference list in
~/Library/Preferences. (Being unable to copy a single file, of course the entire backup failed. How robust.) I don't have the log handy to cut and paste, but that's not a big deal since the log adds essentially no useful information whatsoever, and certainly nothing resembling a cause for the copy failure. Just our old friend, Error 11.
I deleted the file (it was for a trial version of an Aperture plug-in), and then Time Machine complained about another one in the same directory. I moved the directory onto Time Machine's ignore list, and the backup completed fine. I'm not buying the idea that this is a disk failure or pre-failure. There is no other evidence of disk trouble. There is no SATA-subsystem logging of read or write errors. System Profiler lists the S.M.A.R.T. status as "Verified". Before I deleted it, I opened and viewed the file.
Time Machine needs to be fixed.