Hi I installed Wordpress on my old domain that was contain thousand of pages but now webmaster tool is showing 404 errors in big amount.please let us guide which plugin is best that solve this problem or remove that pages that is not exists now. Thanks
Im not sure about plugins but here is the link how to edit your error page. http://codex.wordpress.org/Creating_an_Error_404_Page
My favorite one: http://wordpress.org/extend/plugins/link-juice-keeper/ Do you really need 404 page? This plugin is perfect for blogging, especially if you have thousand of pages. Each time the post of page is not fund it redirect visitors to your homepage.
I think this happen when that days where WordPress got some technical problems. If your pages still has this problem, you better contact a developer.