The Problem
If your SpamAssassin started recognising emails as spam, it's maybe because of the FH_DATE_PAST_20XX issue. For some, to me unknown reason, this started to appear in Spam-Report in 2010.
The Solution
Run these commands after being logged to your server as root:
sa-update
/etc/rc.d/init.d/spamassassin restart
It worked on my Fedora Linux.
February 23, 2010