From my days with playing with Net::SNMP, I remember that I liked the get_next_request more than get_request and all my OIDs start with a dot.
Some working code (which i seem to copy paste a lot):

my ($s,$e)=Net::SNMP->session(-hostname=> $ip, -community =>$community
+);

if (!defined($s)) {
        printf("error: %s.\n", $e);
        exit 1;
}

$oid = ".1.3.6.1.4.1.9.9.42.1.2.1.1.2";
my @args = ( -varbindlist =>  [$oid]);
while ( defined $s->get_next_request(@args) ) {
        $_ = ( keys(%{ $s->var_bind_list }) )[0];

        if (!oid_base_match($oid, $_)) { last; }
        printf("%s => %s", $_, $s->var_bind_list->{$_});
        my @n = split /\./, $_;
        print "  (index: ",$n[$#n],")\n";

        @args = (-varbindlist => [$_]);
}
# Let the user know about any errors
if ($s->error() ne '') {
        print $s->error(),"\n";
}
[download]

Try to see if you understand this small example (read: perldoc it);-)

cheers

PS: I think *your* problem is just that you have to start your OID with a DOT (like the error message says). Nothing more...