form submission with checkbox list I have multiple checkboxs in a form

&lt;input type="checkbox" name="Classification[]" value="Hub Zone"&gt;Hub Zone
&lt;input type="checkbox" name="Classification[]" value="Not Applicable"&gt;Not 


After submit Get info is:

 'Classification' =&gt; 
  array (
    0 =&gt; 'Hub',
    1 =&gt; 'Not Applicable',
  ),


and I get error : array to string conversion on below code

 'Classification'  =&gt; array(AttributeType::Mixed, 'required' =&gt; true, 'label' =&gt; 'Classification')


stack Trace:

PHP notice
Array to string conversion

/home/www/html/www3/craft/storage/runtime/compiled_templates/3d/3df3f71b6051f05e907988ee087f2136f9ad04870a88d4a66539df50db139f6d.php(39)

27         }
28         // line 6
29         if ((array_key_exists("fields", $context) &amp;&amp; twig_length_filter($this-&gt;env, (isset($context["fields"]) ? $context["fields"] : $this-&gt;getContext($context, "fields"))))) {
30             // line 7
31             echo "    ";
32             $context['_parent'] = $context;
33             $context['_seq'] = twig_ensure_traversable((isset($context["fields"]) ? $context["fields"] : $this-&gt;getContext($context, "fields")));
34             foreach ($context['_seq'] as $context["_key"] =&gt; $context["field"]) {
35                 // line 8
36                 echo "        ";
37                 echo twig_escape_filter($this-&gt;env, $this-&gt;getAttribute($context["field"], "label", array()), "html", null, true);
38                 echo ": ";
39                 echo twig_escape_filter($this-&gt;env, $this-&gt;getAttribute($context["field"], "value", array()), "html", null, true);
40                 echo "
41 
42     ";
43             }
44             $_parent = $context['_parent'];
45             unset($context['_seq'], $context['_iterated'], $context['_key'], $context['field'], $context['_parent'], $context['loop']);
46             $context = array_intersect_key($context, $_parent) + $_parent;
47         }
48         // line 12
49         if ((array_key_exists("footer", $context) &amp;&amp; twig_length_filter($this-&gt;env, (isset($context["footer"]) ? $context["footer"] : $this-&gt;getContext($context, "footer"))))) {
50             // line 13
51             echo "
I think your checkboxes need to be as follows:

&lt;input type="checkbox" name="fields[Classification][]" value="Hub Zone"&gt;Hub Zone
&lt;input type="checkbox" name="fields[Classification][]" value="Not Applicable"&gt;Not