Greetings all,
I agree with Roy Johnson about the slashes. you are trying to make @results a reference on the left hand side, which is why you are getting the error.
Here are my suggestions for modifying your code.

my $command = sub { 
    my @returnstring = $d->checklist( text => $text, list => [ @list ]
+ );
    return \@returnstring;
};
my $some_ref = &$command;
[download]

Now if you wanted the array from $d->checklist() to return as a reference itself you might try.

my $command = sub { 
    my $returnstring = \($d->checklist( text => $text, list => [ @list
+ ] ));
    return $returnstring;
};
my $some_ref = &$command;
[download]

However if you already have declared @returnstring outside of the scope of your anonymous sub and you wish to use this sub to modify it then you could simply do something like this...

my @returnstring;
my $command = sub { 
    @returnstring = $d->checklist( text => $text, list => [ @list ] );
};
[download]

again assuming that $d->checklist() returns an array.
A simple way to think of it is that references get assigned to something. So the \ is allowed on the right hand side only.
At least thats what works for me. :)
These examples are untested but I think, as Roy Johnson pointed out, that your slashes are the problem.

-InjunJoel