|my guess would be the /D option with no date given. If backing up static files (programs and static data), the /D is better left off, since the static data should not change (and if it does change, better watch out! after all, why would you need to back up static material? it only needs to be saved once, and if it changes, you prob'ly don't want it anyway as it might have been corrupted)|
If, as is more likely, backing up dynamic files, might be best to 1) check the dates of the files on D: drive, maybe they got set to the future, and of course verify your computer's date/time, 2) try xcopy with all your same options from the command-line, with the added option /L, and see what it gives you.