500.0 Internal Server Error - aspnet_isapi.dll failed in IIS 7.5

If you experience '500.0 Internal Server Error - aspnet_isapi.dll failed' even after trying all possibilities like 'aspnet_regiis -i' etc..., just uninstall IIS and Re-install again, it just works. It is Microsoft:)

I faced this when i installed Framework 4.0, so uninstalled IIS 7.5/Framework4.0 and re-installed both.

Error message when you visit a Web site that is hosted on IIS 7.5: "HTTP Error 404.17 - Not Found"

This article might help, but we need to look for three things particularly

configure the following settings to match the handler requirements:

• .NET Framework Version
• Enable 32-Bit Applications
• Managed Pipeline Mode

Custom(!!!) Basic Authentication

How often we think about using BASIC authentication only to figure out that it is hardwired to windows accounts? So what we have Custom Basic authentication using httpmodules. Excellent article here

One more compelling reason to go for Custom BASIC authentication, it is not tied to  UTF-8(uses ISO-8859-1), hence passing non 8-bit characters doesn't work at all.
http://stackoverflow.com/questions/702629/utf-8-characters-mangled-in-http-basic-auth-username/703341#703341
http://stackoverflow.com/questions/7242316/what-encoding-should-i-use-for-http-basic-authentication
http://greenbytes.de/tech/webdav/draft-reschke-basicauth-enc-latest.html
http://tools.ietf.org/html/rfc2617#section-2