For November 13 and November 16, I started seeing URLS showing up in Webmaster Tools "In Sitemaps" with the error:
"DNS lookup timeout"
For November 19, the Sitemap URL errors now show:
I have no problems reaching the URLs in question. I've contacted my hosting company for my dedicated server (the same company that Webmasterworld uses) and they assure me that everything is fine based on a tool they use. I rely heavily on technical support for these kinds of issues.
I use a couple different tools and it appears that if I do several DNS lookups of my domain in a row, several will be fine and occasionally there will be a DNS timeout. For giggles, I just used the same tool to do several DNS lookups for Webmasterworld and got the same DNS timeout error.
Is Webmaster tools just being flaky or is it possible that there is a broader Network DNS issue going on?
According to Webmaster Tools, I have 120 "In Sitemaps" errors and 453 "Unreachable" errors. It seems foolish to ignore the errors, but I'm running out of ideas to check.