I recently came across an interesting error when using the rdiff-backup program:

Cannot change mtime of /backupdestdir/somedir/rdiff-backup.tmp.23 to 3937075508
problem is probably64-32bit conversion

Turns out the cause of this error is if the date of the file in question has been modified in the future – in my particular case 2094. :-)

You can change the modification date to the current date by running the command “touch filename”.