Matt Cutts Reports Issue With ASP.NET 2 URL Rewriting Bug

IMPORTANT NOTE: This issue does NOT affect vBSEO IIS customers.

It has been reported that doing URL rewrites with ASP.NET 2 causes a HTTP 302 status code for each rewritten page, rather than the required 200 status code.

Quote Originally Posted by Matt Cutts
It sounds as though if this issue (ASP.NET 2 + url rewriting generates a 302 instead of a 200) affects you, your site may drop out of most search engines.
Matt also comments on an upgrade to the Sitemaps console, showing more details on errors Googlebot encounters while crawling your site.

Notes on vBSEO
  • The ASP.NET 2 rewriting problem does NOT affect vBSEO IIS customers.
  • vBSEO is fully compatible with both Apache & IIS; as well as Lighttpd, Zeus and Litespeed
  • vBSEO uses ISAPI rewriting for IIS hosted forums.
For Discussion
  • Have you discovered any Googlebot errors reported in your Google Sitemap's console?
Source:
Matt Cutts: Gadgets, Google, and SEO » ASP.NET 2 + url rewriting considered harmful in some cases