... attribute ... lacks value

Cause:

This is an error show when an attribute contained in a tag does not contain a value and that a value was expected.
Or this can also be due to syntax error in the  HTML tag.

Solution:

Check the definition of the attribute.
Give a value to the tag.
Or correct the wrong/unkown tag.

Sample:

<a> attribute href lacks value

BAD    <a href>My Link</a>
GOOD   <a href="my_link.html">My Link</a>

References:

http://www.w3.org/TR/html4/index/attributes.html