try working with get_next_request() .. it works better ;-)
i'll show sample example which (first of all works) I use to check the memory on cisco routers:

#!/usr/local/bin/perl
#
use Net::SNMP  qw(oid_lex_sort oid_base_match SNMP_VERSION_1 DEBUG_ALL
+);
use strict;


my $ip = scalar @ARGV >= 1 ? $ARGV[0] : "192.168.0.1";
my $community = scalar @ARGV == 2 ? $ARGV[1] : "secret";
my ($s,$e)=Net::SNMP->session(-hostname=> $ip, -community =>$community
+);

if (!defined($s)) {
        printf("error: %s.\n", $e);
        exit 1;
}
print "-"x78,"\n";
print "Search memoryPools for: $ip (community: $community)\n";
print "-"x78,"\n";

my $oid = ".1.3.6.1.4.1.9.9.42.1.1.11";
my @args = ( -varbindlist =>  [$oid]);
while (defined($s->get_next_request(@args))) {
    $_ = (keys(%{$s->var_bind_list}))[0];
    if (!oid_base_match($oid, $_)) { last; }
    printf("rttMonApplFreeMemLowWaterMark:                    %s\n", $
+s->var_bind_list->{$_});
    @args = (-varbindlist => [$_]);
}
$oid = ".1.3.6.1.4.1.9.9.48.1.1.1.6";
my @args = ( -varbindlist =>  [$oid]);
while (defined($s->get_next_request(@args))) {
    $_ = (keys(%{$s->var_bind_list}))[0];
    if (!oid_base_match($oid, $_)) { last; }
    printf("ciscoMemoryPoolFree:                              %s\n", $
+s->var_bind_list->{$_});
    @args = (-varbindlist => [$_]);
}

print "-"x78,"\n";
$s->close();
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