Depends on the kinds of errors being generated. I use wordpress and it does not generate errors like that for me. It may be the theme you are using.
Anyways, invalid markup plays a very minimal role in seo. The primary way it effects things is with site speed. If there are errors that may impact your site's load time then yes it can penalize you a little. But not enough where you will really see that negativity. If the rest of your site is properly optimized you would be fine. It is minor problems that compound and add up which will create a headache for you.
