$projectname needs to be an ARRAY:

Methods

$graph->set_legend(@legend_keys);

    Sets the keys for the legend. The elements of @legend_keys corresp
+ond to the data sets as provided to plot().

    If a key is undef or an empty string, the legend entry will be ski
+pped.
[download]

So
my @projectname = ('Dynamic reconfiguration FY06 Initiative','Rmg Escalation Management Tool');

and

$mygraph->set_legend(@projectname);

HTH.