Internet Information Services 5.0:

SUPPORT SOLUTION:
RAPID PUBLISHING ARTICLES PROVIDE INFORMATION DIRECTLY FROM WITHIN THE MICROSOFT SUPPORT ORGANIZATION. THE INFORMATION CONTAINED HEREIN IS CREATED IN RESPONSE TO EMERGING OR UNIQUE TOPICS, OR IS INTENDED SUPPLEMENT OTHER KNOWLEDGE BASE INFORMATION.Consider the following scenarios.  In Internet Information Services (IIS) 5.0, you create a test.shtml page that uses the PATH_INFO server variable.  You then use an HTTP client like Internet Explorer to send a request to the following type of URL on the IIS server:
            http://iis5server/test.shtml/iis
(http://iis5server/test.shtml/iis)
   
In response to this request, IIS 5.0 will send the client an HTTP 404-File Not Found status error. 
Alternately, in Internet Information Services (IIS) 6.0 you create the same test.shtml page that uses the PATH_INFO server variable.  When a request is then sent to http://iis6server/test.shtml/iis
(http://iis6server/test.shtml/iis)
, IIS 6.0 will respond to the request with an HTTP 200-OK status.
Internet Information Services (IIS) 5.0 and Internet Information Services (IIS) 6.0 handle requests for resources that are mapped to ssinc.dll differently.

This behavior is by-design. A change was made between IIS 5.0 and IIS 6.0 to better serve requests that are handled by ssinc.dll and that use the PATH_INFO server variable.  The change allows files mapped to ssinc.dll to contain a PATH_INFO URI segment appended to the URL of the resource
IIS Server-Side Include Directives
http://msdn.microsoft.com/en-us/library/ms525185.aspx
(http://msdn.microsoft.com/en-us/library/ms525185.aspx)
 
IIS Server Variables
http://msdn.microsoft.com/en-us/library/ms524602.aspx
(http://msdn.microsoft.com/en-us/library/ms524602.aspx)
 
AllowPathInfoForScriptMappings
http://msdn.microsoft.com/en-us/library/ms525840.aspx
(http://msdn.microsoft.com/en-us/library/ms525840.aspx)
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