14503 Google De Indexing VBulletin

Hi I have a vBulletin 3.54 and am using Google sitemap. I a couple of weeks ago I had nearly 800 pages index but now only 300. It shows I have 404 errors of 291 pages not found. All of them have this archive path? archive/[login to view URL] archive/[login to view URL] etc.etc. Also no [login to view URL] file has been found. I need help with this so Google stops De Indexing my pages? I think this should be an easy fix with a tweak and also by adding [login to view URL] file??? Please I need someone with experience.