You have 4 pages with same title tag,so generally this kind of error affects your ranking because google confused to target the correct page for ranking,so to solve this problem you should rename all pages and submit the sitemap again in web master, your error will be solve.

Sounds like you might have an indexing problem. Check your wordpress settings to see if you can "no-index" author pages as they will be duplicates of your page. A great plugin to achieve this would be W3 Total Cache. There are some great tutorials online to assist in configuring the plugin. I would recommend reading blog posts by www.wpbeginner.com

This means all the 4 pages have same title. check once , if same remove based on content

These pages have same title tag.

Only testing can reveal if this is affecting your SEM efforts. Have you contacted Google support?

Google Webmaster Tool>Site Apprerance>HTML Improvement shows my author page as duplicate title tag.

I have 4 pages in my site running on wordpress. The error it shows is like:

http://www.mysite.com/author/username/ | http://www.mysite.com/author/username/page/2/ |

http://www.mysite.com/author/username/page/3/ | http://www.mysite.com/author/username/page/4/

(2,3,4 here represents second, third and fourth page)

Anyone can tell me if it is effecting my SEO and what would be the solution.