500 Internal Server Error

The gory details:
Error: Not array - for
***  in function &quot;array_get_keys&quot;
***  line: {L1}[-1] = {L2}
***  call: array_get_keys (&quot;&quot;)
***  call: array_length (&quot;&quot;)

evaluating argument for _ixloop_  around

to=&quot;&lt;%= array_length(f.&quot;cat_story&quot;) %&gt;&quot;&gt;
                      &lt;% local i = hix_loop_index()-1 %&gt;
                      &lt;tr&gt;
                        &lt;td valign=&quot;top&quot;&gt;
                          &lt;ta