missing <...>

Cause:

A tag is missing in a mandatory context.

Solution:

Check in which context should the tag be defined.

Tag
 Bad
 Good
<tr>
 <table>
  <td>abc</td>
</table>
 <table>
  <tr>
     <td>abc</td>
  </tr>
</table>
...


References:

W3c tags: http://www.w3.org/TR/html4/index/elements.html