$complete_match must be a ref to a AoH (array of hashes) for a <tmpl_loop>

Consider:

my $complete_match = $sth->fetchall_arrayref({});
$template->param(someloop=>$complete_match);

HTML:
<tmpl_loop someloop>
   <tmpl_var column1><tmpl_var column 2> etc...
</tmpl_loop>
[download]

Update: That error can also be caused by naming your form element the same name as your tmpl_loop name. They have to be different.