On Page SEO

See problems Google had crawling your site

Google discovers sites by following links from page to page (called "crawling"). The Crawl Errors page shows problems that we encountered during the crawl process. There may be a problem with your page itself (a page may be missing or corrupted, or blocked from crawlers), or a problem with your web server might be preventing Google from accessing your URLs.

That's why we recommend regularly checking the Crawl errors page in Webmaster Tools. Addressing these problems, where possible, can help improve both your site and how it's indexed by Google.
Crawl errors :
The Crawl errors page provides details about the URLs in your site that we tried to crawl but could not access. The Mobile crawl errors page provides details about problems we encountered crawling URLs on your mobile website.

In addition to listing any URLs we had difficulty crawling, we'll list the type of problem and, where possible, list the page or pages on which we found the error.

Possible errors include:

    * Not found
    * URLs not followed
    * URLs restricted by robots.txt
    * URLs timed out
    * HTTP errors
    * URL unreachable
    * Soft 404s

Note: We can't list information about URLs we haven't recently crawled.