What is mean by Ethical Seo and soft 404 error ?
 

Pls, help me in the difference between SEO and ethical SEO and also a difference between 404 error and soft 404 error?

Based on a quick check of the URLs you list it looks like these pages are being incorrectly flagged as soft 404 pages. Since this feature was just released we are still working on improving our detection of true soft 404 pages. In the near term you should see the number of legitimate pages on your site disappear from the soft 404 crawl errors report. So please check back in with Webmaster Tools over the next few weeks and if you continue to see a high number of pages on site improperly listed as soft 404s you can post the details to this thread and we'll investigate further.

As a result, the page may be listed in search results, and search engines will continue trying to crawl that non-existent URL instead of spending time crawling your real pages.