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So I pruned my vbulletin forum the other week and now webmaster tools detects over 4000 urls as not found.  Is there a solution to this?  Is this something that could negatively effect rankings?  Any ideas?

My website, www.rcnightmare.com has a forum, the most popular entry point for seo traffic.  I have tried unsuccessfully to really make the forum's content outweigh the actual content of the "forum" itself.  For example google analytics says "post" is my strongest keyword across the site. the forums url is www.rcnightmare.com/forum, I am looking for some answers from people familiar with Vbulletin for things I can change to help this

Ok, so I am finally focusing more on SEO of my hobby website as I am notice the relavent keywords are not really onsite what I want, for example, according to analytics "post" is my most popular  keyword which I assume is from the vbulletin forum. My question today is that according to the moz scan, my forum has too many external links, my question is what are some measures I can do whether within the vbulletin forum or custom coding to reduce the amount of links/increase power? www.rcnightmare.com