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There are a few reasons this can happen. Each tool crawls the web at different times and see different things. I would recommend at least investigating any issues you find regardless of which tool you used to discover it. Personally, I would pay good money for a tool from Google which used their algorithms and data, but that isn't an option so we do the best we can with the available tools. Google WMT and SEOmoz crawl reports are two parts of that solution for me.

I've done as you suggested. I came across the issue after running a report that showed 40 links with 302 status-all turned out to be trackbacks. While the above advice takes care of the future, is there any harm in having these existing 302 trackbacks, or any advantage in making them 301s? Thank you, Dan

Hi Josh, If you have a list of actual URLs which always return a 500 Error, the problem is a bug in the code. You should send the list of URLs to your developer and ask him/her to fix them. Often, once a bug is identified and fixed, it will correct all or most of the errors. If you check the URLs and find that the 500 Errors are intermittent (sometimes OK, sometimes returning an error), you should  take a look at this question I answered about random 500 Errors. Hope that helps, Sha

Well, over these many people consider it fits deceived. Recently I did a 301 from a site that had a lot of anchors a keyword to another new domain. The site with many anchors was not yet well ranked. This new Domain began Rank even without a good on-page optimization for that keyword and no direct link back. I suppose it happened because the strength of anchors contained in the old domain. So in my conception, 301, transfers the force of anchor texts.

<base> allows you to set the default attributes for links on the page. For example if I set <base href="http://www.mydomain.com/"> then I can make a link to and it will point to http://www.mydomain.com/mypage.html I believe this magic happens on the web server before the page is sent to the browser, making it a safe practice for SEO.