For IIS6.0 users, the AspMaxRequestEntityAllowed property specifies the maximum number of bytes allowed in the entity body of an ASP request. If a Content-Length header is present and specifies an amount of data greater than the value of AspMaxRequestEntityAllowed, IIS returns a 403 error response.
This property is related in function to MaxRequestEntityAllowed, but is specific to ASP request. Whereas you might set the MaxRequestEntityAllowed property to 1 MB at the general World Wide Web Publishing Service (WWW Service) level, you may choose to set AspMaxRequestEntityAllowed to a lower value, if you know that your specific ASP applications handle a smaller amount of data.
Open your metabase.XML which is located in c:\Windows\System32\Inetsrv find the line "AspMaxRequestEntityAllowed" and change it to "1048576". This is 1MB - of course you can enter another value to suite your needs.
NOTE: Before you edit the file, be sure to stop the IIS service first or else you won't be able to save the file.