Here is the error message from procmail: 
 
Can't use an undefined value as an ARRAY reference at 
/usr/lib/perl5/vendor_perl/5.8.0/Mail/SpamAssassin/Dns.pm line 303.  
 procmail: Program failure (70) of "/usr/bin/spamassassin"  
 procmail: Rescue of unfiltered data succeeded 
 
Someone reported this error on the Gentoo forums.   I suggested replacing line 303 
of Dns.pm: 
 
my $rules = join(",", @{$query->[RULES]});  
 
with: 
 
my $rules = join(",", @{$query->[RULES] || [] }); 
 
and this seemed to have fixed the problem.