Brother tachyon has the right answer above. If you'd like to figure out stuff like this for yourself, the B::Deparse module is very handy:

$ perl -MO=Deparse -e 'Add_Delta_Days( map{$cgi->param($_)} qw(eYear e
+Month eDate), 1)'
Add_Delta_Days(map({$cgi->param($_);} ('eYear', 'eMonth', 'eDate'), 1)
+);
-e syntax OK
$
$ perl -MO=Deparse -e 'Add_Delta_Days( (map{$cgi->param($_)}qw(eYear e
+Month eDate)), 1)'
Add_Delta_Days(map({$cgi->param($_);} 'eYear', 'eMonth', 'eDate'), 1);
-e syntax OK
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Note where it put the parentheses.