13 validation errors & 1 warning W3C markup

I have a client who has enlisted the help of an SEO expert, they have asked me to remove all the errors which have come back from W3C Validator.

Could you advise if there is a problem with the code or is it something I have done? I notice that your demo theme http://themes.themeton.com/marvel/ has 20 Errors and 1 Warning.

I really need some support with this,

Thanks in advance,

Sam http://bestsolicitorsllp.co.uk