I'd say use -v to get verbose output (maybe even -vv...not sure if verbosity, verboseness, whatever, is incremented in rsync). Redirect output to file if necessary. This may list the specific files that aren't being transferred, and should give you a better idea of why the error is occurring.
Perhaps symlinks aren't being followed...in that case, try the -l option.
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( o_
/ >) My 84-year-old non-techy mom uses Debian Linux. It ain't that hard.