- Stop the IIS Admin service (and any services that depend on it)
- Open C:WINDOWSsystem32inetsrvMetaBase.xml in notepad or your favorite XML Editor. DELETE the line that reads ‘Enable32BitAppOnWin64=”TRUE”‘
- Start -> Run -> iisreset
See this post for creating an ASHX handler in ASP.NET. It explains why to use a handler and not an ASPX page for this situation.