GG Webmaster Tools count over 1,000 404 errors for our website. 90% of the errors do not exist any more. Can it affect my keywords rankings or website authority? What can I do to reduce the number of the errors?
What kind of error it is? Did you move your site or removed any page from your site or something? (or modified). is it giving you lot of 404 error or 301 or 502?
If you have access to the links pointing to the 404s fix the problem links tell Google to fetch the fixed page again, and delete the error listing, if the problem links are gone it's not a concern delete the error listing. What's left, create a 301 redirect.