I have been getting some weird errors in Google Webmaster Tools. I have a bunch of 404 errors which are from old pages linking to old pages. Both the old pages being linked to and from have since been removed and now are returning 404 headers.... Any ideas why Google just doesn't update it's details sometimes?
Redirect all main pages using 301 redirection by making/writing code in .htaccess file and remove all the old URL form GWT. 301 redirection gives all the credit of old page to new page.
The problem you may have is there may be links still pointing to those old URL's. When you mark the URL's as fixed it removes them but brings up a message saying they may reappear if the problem persists. You should have a read through your website sitemap.xml to check if those domains are still there and also check to see if there are any internal links pointing to the pages that now show the 404 errors. If you have external links pointing to those domains you should look into putting 301 redirects in place through your .htaccess file so that the traffic is diverted to the correct page which will also fix the Google Webmasters error.
All pages have been 301'd and the old pages are still showing up. There are probably old inbound links pointing to the pages, but I can't really do anything about those. It's not really a huge issue but is just annoying and is definitely a sign that Google isn't happy with me at the moment
Redirect your old pages to new pages using 301 redirect method .if you don't have new pages for redirecting old pages then make one 404 error page & redirect all old pages to that page. but don't redirect all pages to home page that is not good .
Make correction in your pages if the pages still have old page links then remove all the old links from GWT where 404 or 401 error links are showing.