Your SEO crawl has timed out due to an known error

Hi ,im using smart crawl and keep getting this error "Your SEO crawl has timed out due to an known error. Please try again or contact support."
also my site's sitemap isn't accessible ( i getting error 404) but in smartcrawl shows it's Your sitemap is available at /sitemap.xml

what shall i do?

with regards

Reza