[marcmac]

This looks like a bug on our part.

Here's the workaround:

Edit /opt/zimbra/bin/sa-learn, and look for this line:
my $DEF_RULES_DIR = '/usr/share/spamassassin'; # substituted at 'make' time

Change that to:

my $DEF_RULES_DIR = '/opt/zimbra/conf/spamassasin';

And the errors should go away.