Your 'style => "points"' is misplaced. If you want points to indicate your data on the chart, you need to put that in the dataset object, not the chart object.

This works for me:

use strict;
use warnings;

use Chart::Gnuplot;

my @rtppackettimeinms = (1,2,3,4,5);
my @scaledpayloadsize = (1,2,3,4,5);

my $chart = Chart::Gnuplot->new(
    terminal=>'dumb',
#    output =>"temp.png",
    title=>"RTPTSDiff vs ScaledPayloadSize",
    xlabel=>"PacketArrivalTime ms",
    ylabel=>"ScaledPayloadsize"
);

my $dataset = Chart::Gnuplot::DataSet->new(
    style => "points",
    xdata => \@rtppackettimeinms,
    ydata => \@scaledpayloadsize
);

$chart->plot2d($dataset);
[download]

NOTE: I commented 'output =>"temp.png"' and replaced with 'terminal=>dumb' to get the brilliant ASCII art you see below proving I get output and not the error you're seeing.

VinsWorldcomC:\Users\VinsWorldcom\tmp> 1059602.pl

                         RTPTSDiff vs ScaledPayloadSize

    5 ++-------+-------+--------+--------+-------+--------+-------+-------+A
      +        +       +        +        +       +        +       +        +
  4.5 ++                                                                  ++
      |                                                                    |
    4 ++                                                  A               ++
      |                                                                    |
  3.5 ++                                                                  ++
      |                                                                    |
    3 ++                                 A                                ++
      |                                                                    |
      |                                                                    |
  2.5 ++                                                                  ++
      |                                                                    |
    2 ++               A                                                  ++
      |                                                                    |
  1.5 ++                                                                  ++
      +        +       +        +        +       +        +       +        +
    1 A+-------+-------+--------+--------+-------+--------+-------+-------++
      1       1.5      2       2.5       3      3.5       4      4.5       5
                              PacketArrivalTime ms

BTW, LOVE Chart::Gnuplot! You may also deduce from the command prompt above, I'm doing this on Windows 7 x64 with Strawberry Perl 5.16.1 and gnuplot 4.6 patchlevel 3.

Says ...expecting 'data',... but your code only has xdata ...

So I think thats it :)