Are any of the dates for your pk3 files later than 12/11/01? If you've installed the patch, pak6 will probably be the date of your install (01/21/02 or later).
If any of the dates are later than 12/11, the pak file may be corrupted. If all else fails, reinstall the game (copy your saved games first and don't open them until you've re-installed the patch, if you have the patch installed now). Good luck.
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