FH_DATE_PAST_20XX scores on all mails dated 2010 or later.
There was a bug in SpamAssassin that hit Jan 1st, 2010. All emails were getting marked with the above error in SpamAssassin, and it was adding 3.5 to the spam score, thus getting blocked by most standard spamassassin configs.
To fix this, simply run sa-update from a linux command line.