I played around with this a bit and (without actually verifying the math) ended up with the following:

#!/usr/bin/perl
use strict;
use Date::Manip;

my $start = Date::Manip::ParseDate('2013-10-03 00:00:00');
my $end = Date::Manip::ParseDate('2013-12-09 00:00:00');
print "$start\n";
print "$end\n";

#Standard Days
my $standard_delta = Date::Manip::DateCalc($start,$end,1);
print "$standard_delta\n";
my $standard_days = Date::Manip::Delta_Format($standard_delta,2,%dyd')
+;
print "$standard_days\n";

#Business Days
my $business_delta = Date::Manip::DateCalc($start,$end,2);
print "$business_delta\n";
my $business_days = Date::Manip::Delta_Format($business_delta,2,'%dyd'
+);
print "$business_days\n";
[download]

With output that looks like:

2013100300:00:00
2013120900:00:00
+0:2:+0:6:0:0:0
66.87375
+0:2:+0:+4:0:0:0
64.87375
[download]

Note: that I am using a newer version than you state that you are, but as close as I can tell from a cursory glance through the CPAN docs, the functionality has not changed. (I may be wrong about that, but it will only take a second to copy the above and try it. If I am wrong, you waste a copy/paste ->save->run amount of time, not much more...).

Hope that is helpful... Update: Changed format directive from '%dydt' to '%dyd', thus changing the output to exclude the 't' from the end of the calculated days.