'<' + '/' + letter not allowed here

Cause:

The 2 characters '</' have been detected in a wrong place.

Solution:

In most case, this is due to wrong javascript:

BAD   <document.write('</h1>');
GOOD  <document.write('<\/h1>');

References:

W3C faq : http://validator.w3.org/docs/help.html#faq-javascript
HtmlHelp: http://www.htmlhelp.com/tools/validator/problems.html#script