On his blog, Bill has posted about a patch for IIS7 running on a Windows Vista machine that corrects an issue with applications that send multiple response headers.

Today we released a patch for IIS7 in Windows Vista that addresses an issue we've seen with CGI applications (especially PHP applications that use the built-in CGI component). The typical symptom is an application that runs using CGI and is unable to support multiple "cookies" for authentication or personalization.

He also links to the Microsoft Knowledge Base article on the topic and to the download for the patch.