Attribute about not allowed on element article at this point While i checked the markup of my drupal-7 site in http://validator.w3.org/check
it shows me a error:

error Details:
Attribute about not allowed on element article at this point.

I have checked my markup as well as all the functionality that are running properly. Why i am getting this error?
It looks like there is a markup error somewhere whereby you have an &lt;article&gt; tag with an about attribute (i.e. &lt;article class="my-class" about="blah"&gt;).

I would imagine the site is working fine as the attribute will just be ignored if it's not applicable, so I'd find the page and line from the validator error and double check your markup.

You could also try running it past the newer HTML5 W3C validator at http://validator.w3.org/nu/ just in case.