<...> inserting "..." attribute

Cause:

A mandatory attribute for this tag is not defined.

Solution:

Check the definition of the tag. Look for the required attributes.
Add the requested attribute.

Sample: <script> inserting "type" attribute

The <script> tag has a required attribute type.

BAD   <script>
BAD   <script language="Javascript">
GOOD  <script type="text/javascript">

Sample: <style> inserting "type" attribute

The <style> tag has a required attribute type.

BAD   <style>
GOOD  <style type="text/css">

References:

W3C tags: http://www.w3.org/TR/html4/index/elements.html