A concise working code example is always best!

My guess is that you are seeing something like:

#! /usr/bin/perl
use warnings; use strict;

use HTML::Template;
use Data::Dumper;

my $text = "<TMPL_LOOP foo>bar=<TMPL_VAR bar>\n</TMPL_LOOP>";

my $template = HTML::Template->new(scalarref => \$text,
                                   loop_context_vars => 1);

my @a = ({bar => 10}, {bar => 20});

$template->param(foo => \@a);

my @array = $template->param('foo');

print Dumper(@array);

$template->param(foo => \@array);
$template->output;
[download]

$VAR1 = [
          {
            'bar' => 10
          },
          {
            'bar' => 20
          }
        ];
HTML::Template->output() : fatal error in loop output : Not a HASH ref
+erence at /usr/share/perl5/HTML/Template.pm line 3059.
[download]

HTML::Template's param method is returning a scalar reference, so by assigning the return value to an array, you end up with a single element array. That element being the array reference.

The \@array expression then adds another level of indirection. You end up with an array reference to your one element array; the element being an array reference.

You need to work with a returned array reference. Example follows:

#! /usr/bin/perl
use warnings; use strict;
use HTML::Template;
use Data::Dumper;

my $text = "<TMPL_LOOP foo>bar=<TMPL_VAR bar>\n</TMPL_LOOP>";

my $template = HTML::Template->new(scalarref => \$text,
                                   loop_context_vars => 1);
$template->param(foo => [{bar => 10}, {bar => 20}]);

my $array_ref = $template->param('foo');
if ($array_ref) {
    print Dumper($array_ref);
    print Dumper($array_ref->[1]);
    #
    # add a new element
    #
    push (@$array_ref, {bar => 30});

    $template->param(foo => $array_ref);
}
print $template->output;
[download]

Also be aware of a potential trap with the one argument usage of param method. In the above example, if foo is deleted from the template, this method will returned undef rather than the array. I tend to avoid using it for this reason.

Update: Added loop_context_vars => 1 to HTML::Template->new(...). Now getting exactly the same error message as the OP.

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